In an OSPF network, each router maintains a link state database that
describes the topology of the autonomous system (AS). The database
contains the local state for each router in the AS, including the router’s
usable interfaces and reachable neighbors. Each router periodically checks
for changes in its local state and shares any changes detected by flooding
link state advertisements (LSA) throughout the AS. Routers synchronize
their topological databases based on the sharing of information from LSAs.
From the topological database, each router constructs a shortest-path tree ,
with itself as the root. The shortest-path tree gives the optimal route to each
destination in the AS. Routing information from outside the AS appears
on the tree as leaves.
OSPF routes IP traffic based solely on the destination IP address and
subnet mask, and IP TOS contained in the IP packet header.
The autonomous system (AS) can be subdivided into areas that group
together contiguous networks, routers connected to these networks, and
attached hosts. Each area has its own topological database, which is
invisible from outside the area. Routers within an area know nothing of the
detailed topology of other areas. Subdividing the AS into areas significantly
reduces the amount of routing protocol traffic as compared to treating the
entire AS as a single link state domain.
Feature Updates Update type Transport Authentication Metric Metric type Topology size Convergence RIPv2 Periodic Broadcast/Multicast UDP Simple and MD5 Hops Distance vector IS-IS Incremental L2 Multicast Layer 2 Simple and MD5 Cost Link-state OSPF Incremental L3 Multicast IP Simple and MD5 Cost Link-state Small/Medium Slow Fast Large Fast Large
OSPF — Path Determination
OSPF uses SPF for path determination.
SPF uses cost values to determine the best path to a destination.
RTR-A RTR-C RTR-B Cost 0 Cost 10 Cost 125 Cost 125 Cost 135 RTR-A 10.0.0.0 – Cost 260 via RTR C *10.0.0.0 – Cost 135 via RTR B * = Best path 10.0.0.0
Calculating Link Cost
Cost = reference-bandwidth ÷ bandwidth
The default reference-bandwidth is 100 000 000 kb/s or 100 Gb/s.
The default auto-cost metrics for various link speeds are as follows:
10-Mb/s link default cost of 10 000
100-Mb/s link default cost of 1000
1-Gb/s link default cost of 100
10-Gb/s link default cost of 10
The cost is configurable.
Interfaces must be configured in an OSPF area.
Verify that adjacencies are formed with neighbors.
Verify that routes are in the routing table.
Open Shortest Path First (OSPF) Section 2 — OSPF Packet Types
This section describes the operation of OSPF:
OSPF packet types
Communication with other routers
Election and purpose of the designated router
OSPF — Multicast Addressing
Specially reserved addresses for OSPF:
188.8.131.52: All routers that speak OSPF on the segment
184.108.40.206: All DR/BDRs on the segment
IP multicast addresses use the lower 23 bits of the IP address as the low-order bits of the MAC multicast address 01-005E-XX-XX-XX.
220.127.116.11 = MAC 01-00-5E-00-00-05
18.104.22.168 = MAC 01-00-5E-00-00-06
OSPF — Generic Packet
OSPF packets use protocol number 89 in the IP header.
OSPF is its own transport layer.
Alcatel-Lucent Interior Routing Protocols and High Availability IP header protocol ID 89 = OSPF Link header IP header OSPF packet types Link trailer
OSPF — Packet Header
The OSPF packet is divided into the following fields.
Each field is always present in any OSPF packet sent.
Version number Type Packet length Router ID Area ID Check- sum Authen-tication type Authen-tication Data
OPSF — Packet Types
OSPF database descriptor
OSPF link-state request
OSPF link-state update
OSPF link-state ACK
Alcatel-Lucent Interior Routing Protocols and High Availability
OSPF — Authentication
OSPF supports three types of authentication:
No authentication (default)
OSPF — Hello Packet Overview Hello * These aspects of the hello packet must match for all neighbor routers on the segment.
The hello packet aids in establishing adjacencies.
Hello packet information Router ID Area ID* Authentication and Password* Hello and dead intervals * Stub area flag* Priority value DR IP address BDR IP address Neighbors
OSPF — Hello Packet Format Checksum Router ID Area ID AuType Version# 1 Packet length Authentication Authentication Network mask Hello interval Options Rtr Pri Router dead interval Designated router Backup designated router Neighbor 0 31
OSPF — Adjacencies
Establishing an adjacency:
22.214.171.124 126.96.36.199 (1) (2) (3)
No neighbors known
(2) Hello, RID= 188.8.131.52 I see neighbor 184.108.40.206 2-Way Hello (4) Hello, RID=220.127.116.11 I see neighbor 18.104.22.168
OSPF — Database Descriptor Packet Format Checksum Router ID Area ID AuType Version# 2 Packet length Authentication Authentication Interface MTU Options DD sequence number LSA header 0 0 0 0 0 M MS 0 31
OSPF — Adjacencies (continued)
Establishing an adjacency:
22.214.171.124 126.96.36.199 1/1 1/1 (1) (2) (3) (4) (1) DBD: RID = 188.8.131.52 (2) DBD: RID = 184.108.40.206 Exchange Exstart (3) DBD: Summary of all networks known (4) DBD: Summary of all networks known (Higher RID begins)
OSPF — Link-State Request Packet Format Checksum Router ID Area ID AuType Version# 3 Packet length Authentication Authentication LS type Advertising router Link-state ID 0 31
OSPF — Link-State Update Packet Format Checksum Router ID Area ID AuType Version# 4 Packet length Authentication Authentication No. of Advertisements List of LSAs 0 31
OSPF — LSR and LSU Exchange
Establishing an adjacency:
220.127.116.11 18.104.22.168 E0 E0 (1) (2) (3) (4) (1) LSR: Send information for the Following networks… (2) LSR: Send information for the following networks… (3) LSU: Here is what you requested (4) LSU: Here is what you requested
OSPF — Completing the Exchange of Information
Establishing an adjacency:
22.214.171.124 126.96.36.199 E0 E0 (1) (2) (3) (4) (1) ACK: Thanks for the information (2) ACK: Thanks for the information (3) Hello (4) Hello Full adjacency
On point-to-point links, there is no need for a DR or BDR.
All packets are sent via IP multicast address 188.8.131.52.
Usually a leased-line (i.e., HDLC, PPP) segment
Can be configured on point-to-point Ethernets
OSPF — Point-to-Point Segments RTR - A RTR - C RTR - B Network 184.108.40.206/24
OSPF — LAN Communication
Election of the DR and BDR in multi-access networks:
C 220.127.116.11 D 18.104.22.168 E 22.214.171.124 A 126.96.36.199 B 188.8.131.52
Each router sends hellos.
The router with the highest priority is the DR.
If all priorities are the same, the DR is the router with the highest RID.
RTR-A Has the highest RID, so it will be the DR RTR-B Has the second highest RID, so it will be the BDR
OSPF — Exchanging Updates in a LAN
Election of the DR and BDR in multi-access networks:
RTR-C 184.108.40.206 D 220.127.116.11 E 18.104.22.168 RTR-A (DR) 22.214.171.124 RTR-B (BDR) 126.96.36.199
Routers use the 188.8.131.52 IP address to send updates to the DRs.
The BDR monitors the DR to ensure that it sends updates.
The DR uses 184.108.40.206 to send updates to all OSPF routers.
RTR-C sends update to All DRs using IP address 220.127.116.11 RTR-A sends update to All OSPF routers using IP address 18.104.22.168
OSPF — Adding a Router to a LAN DR BDR New router * The new router uses IP address 22.214.171.124 to send a hello. All routers will see the hello. Hello, RID = 126.96.36.199 I see no others RID – 188.8.131.52 RID – 184.108.40.206 RID – 220.127.116.11
OSPF – Learning Which Is the DR/BDR in a LAN DR BDR New router * The new router waits to see if any other router speaks OSPF. If so, it checks to see if a DR and BDR are present. Hello, RID = 18.104.22.168 I see 22.214.171.124 and 126.96.36.199 RID – 188.8.131.52 RID – 184.108.40.206 RID – 220.127.116.11
OSPF — Advertising a New Network DR BDR New router * The new router sends LSAs about networks to the DR and BDR via the 18.104.22.168 (all DRs) multicast address. LSA 22.214.171.124 RID – 126.96.36.199 RID – 188.8.131.52 RID – 184.108.40.206
OSPF — Updating Peers about a Network Change DR BDR LSA 220.127.116.11 * The DR sends an update to all routers about the new network learned. It waits for an ACK from all routers. RID – 18.104.22.168 RID – 22.214.171.124 RID – 126.96.36.199 New router
OSPF — Network Change Flow DR BDR * The DR sends an update to all routers about the network change. It waits for an ACK from all routers. LSA 1 2 3 LSA 188.8.131.52 LSA 184.108.40.206
Open Shortest Path First (OSPF) Section 3 — Adjacency Case Study
Adjacency between rtr4 and rtr5 rtr5 rtr4 220.127.116.11 18.104.22.168 10.10.1.0/30 .1 .2 10.10.1.4/30 .5
Adjacency — Exstart State rtr5 rtr4 22.214.171.124 126.96.36.199 10.10.1.0/30 .1 .2 10.10.1.4/30 .5 1 OSPF Version : 2 Router Id : 188.8.131.52 Area Id : 0.0.0.0 Checksum : 7c0e Authentication : Null Authentication Key: 00 00 00 00 00 00 00 00 Packet Type : DB_DESC Packet Length : 32 Interface MTU : 1500 Options : 000042 Flags : 7 Sequence Num : 77793 " OSPF Version : 2 Router Id : 184.108.40.206 Area Id : 0.0.0.0 Checksum : 865e Authentication : Null Authentication Key: 00 00 00 00 00 00 00 00 Packet Type : DB_DESC Packet Length : 32 Interface MTU : 1500 Options : 000042 Flags : 7 Sequence Num : 75667 " 1 2 2
Adjacency — Exchange State rtr5 rtr4 220.127.116.11 18.104.22.168 10.10.1.0/30 .1 .2 10.10.1.4/30 .5 OSPF Version : 2 Router Id : 22.214.171.124 Area Id : 0.0.0.0 Checksum : bfff Authentication : Null Authentication Key: 00 00 00 00 00 00 00 00 Packet Type : DB_DESC Packet Length : 192 Interface MTU : 1500 Options : 000042 Flags : 0 Sequence Num : 77793 Link ID : 126.96.36.199 LSA Type : RTR Area ID : 0.0.0.0 Router ID : 188.8.131.52 Seq. Num : 8000003f Age : 0 Length : 72 Checksum : 4c64 Option Bits Set: E 02 ...
Adjacency — Exchange State (continued) rtr5 rtr4 184.108.40.206 220.127.116.11 10.10.1.0/30 .1 .2 10.10.1.4/30 .5 OSPF Version : 2 Router Id : 18.104.22.168 Area Id : 0.0.0.0 Checksum : 93f9 Authentication : Null Authentication Key: 00 00 00 00 00 00 00 00 Packet Type : DB_DESC Packet Length : 52 Interface MTU : 1500 Options : 000042 Flags : 1 Sequence Num : 77794 Link ID : 22.214.171.124 LSA Type : RTR Area ID : 0.0.0.0 Router ID : 126.96.36.199 Seq. Num : 80000003 Age : 8 Length : 48 Checksum : 51b5 Option Bits Set: E 02 ...
Adjacency — Exchange State (continued) OSPF Version : 2 Router Id : 188.8.131.52 Area Id : 0.0.0.0 Checksum : 7af8 Authentication : Null Authentication Key: 00 00 00 00 00 00 00 00 Packet Type : LS_REQ Packet Length : 120 LS Type : 1 Link State Id : 184.108.40.206 Advt Router : 220.127.116.11 ... rtr5 rtr4 18.104.22.168 22.214.171.124 10.10.1.0/30 .1 .2 10.10.1.4/30 .5
Adjacency — Exchange State (continued) rtr5 126.96.36.199 188.8.131.52 10.10.1.0/30 .1 .2 10.10.1.4/30 .5 OSPF Version : 2 Router Id : 184.108.40.206 Area Id : 0.0.0.0 Checksum : 1e65 Authentication : Null Authentication Key: 00 00 00 00 00 00 00 00 Packet Type : LS_UPD Packet Length : 100 Num of LSAs : 1 Link ID : 220.127.116.11 LSA Type : RTR Area ID : 0.0.0.0 Router ID : 18.104.22.168 Seq. Num : 80000040 Age : 1 Length : 72 Checksum : f99c Option Bits Set: E 02 # Links : 4 Flags: 1 Link Type : P2P Link Nbr Rtr ID : 22.214.171.124 I/F Addr : 10.10.1.1 Metric-0 : 1000 2 Link Type : Stub Net Network : 10.10.1.0 Mask : 255.255.255.252 Metric-0 : 1000 3 Link Type : Stub Net Network : 126.96.36.199 Mask : 255.255.255.255 Metric-0 : 0 4 Link Type : Transit DR IP Addr : 10.10.0.1 I/F Addr : 10.10.0.2 Metric-0 : 1000
Adjacency — Full Adjacency State rtr5 rtr4 188.8.131.52 184.108.40.206 10.10.1.0/30 .1 .2 10.10.1.4/30 .5 OSPF Version : 2 Router Id : 220.127.116.11 Area Id : 0.0.0.0 Checksum : 678d Authentication : Null Authentication Key: 00 00 00 00 00 00 00 00 Packet Type : LS_ACK Packet Length : 44 Link ID : 18.104.22.168 LSA Type : RTR Area ID : 0.0.0.0 Router ID : 22.214.171.124 Seq. Num : 80000040 Age : 1 Length : 72 Checksum : f99c Option Bits Set: E 02 ...
Open Shortest Path First (OSPF) Section 4 — OSPF Areas, Networks, and LSAs
In a large enterprise with many routers and networks, the LSDB and
routing tables become large. This is not advantageous because:
· Large routing tables consume memory and result in more CPU cycles
being needed to make a forwarding decision.
· Large LSDBs consume memory.
· The processing of LSAs is CPU-intensive.
Dividing the network into OSPF areas can reduce these undesirable side
Some advantages of implementing OSPF areas are as follows:
· Routers internal to the area incur less overhead.
· The impact of a topology change is localized to the area in which it
occurs. Although the change is advertised outside the area, the
processing of LSA, and consequent modification of the SPF tree,
requires less CPU overhead.
· With careful network address planning, networks within an area can be
advertised in the form of a summary. This reduces the amount of
processing on all routers external to the area, as well as reducing the
size of the routing table.
OSPF — Area Overview Area 0 Area 1 Area 2 Autonomous System
Areas allow for summarization
Reduced flooding of topology changes
Hierarchal topology design
RTR-A RTR-B RTR-C RTR-D RTR-E
OSPF — Types of Routers Area 0 Area 1 Area 2 Autonomous System
RTR-A is a backbone router.
RTR-B and RTR-C are ABRs.
RTR-D and RTR-E are intra-area routers .
RTR-A RTR-B RTR-C RTR-D RTR-E
OSPF — Link-State Advertisement Types Link-state type 1 2 3 4 5 7 8 9, 10, 11 OSPF function Router link states Network link states Summary link states ASBR link state External link advertisement NSSA external link state External attributes for BGP Opaque LSA
OSPF — Type 1 (Router) LSA
Each router in an area generates a router LSA for each area it belongs to.
— Lists directly attached links
— Advertised with the IP prefix and mask assigned to link
Sourced by the RID of the originating router
Flooded within the area only; does not leave the area
Advertised by all OSPF routers
OSPF – Type 2 (Network) LSA
One LSA for each broadcast or NBMA network in an area
Lists the subnet mask of the link and all attached routers
Advertised by the DR
Flooded within the area only; becomes a type 3 LSA on exit
Floods summary network information to other areas
States the network number and mask
Advertised by the originating area ABR
Goes to all areas within the autonomous system
OSPF – Type 3 (Summary) LSA Area 1 Area 0
A stub area is configured at the edge of the OSPF routing domain and has
only one ABR. A stub area does not receive LSAs for routes outside its
area, reducing the size of its link state database. A packet destined outside
the stub area is routed to the ABR, which examines it before forwarding
the packet to its destination. The network behind a passive interface is
treated as a stub area, and does not form adjacencies. It is advertised into
the OSPF area as an internal route.
Not so stubby area (NSSA)
A not so stubby area prevents the flooding of external LSAs into the area
by replacing them with a default route. An NSSA can import small stub
(non-OSPF) routing domains into OSPF. Like stub areas, NSSAs are at the
edge of an OSPF routing domain. Non-OSPF routing domains are attached
to the NSSAs, forming NSSA transit areas. Accessing the addressing
scheme of small stub domains permits the NSSA border router to also
perform manual aggregation.
OSPF – Stub and Stub, No Summary
Stub area (a single area that is a dead end):
The ABR blocks all type 5 LSAs and sends the default route.
Stub area, no summary;
The common industry term is “totally stubby”.
The ABR blocks all type 3, 4, and 5 LSAs and sends the default route.
Area 0 Area 2 Stub No type 3, 4, or 5 LSA; default route instead No type 5 LSA5; default route instead Area 1 Stub, no summaries
OSPF — LSA Sequence Numbers
Each sequence number is a 32-bit value represented as a hex number.
The sequence number -N (0x80000000) is reserved (and unused). This leaves — N + 1 (0x80000001) as the smallest number (oldest information).
Sequence numbers increment each time an LSA is flooded for that specific network.
The higher the sequence number, the more trusted the information.
The counters roll over when the maximum value is reached.
OSPF — Packet Processing
Dealing with topology changes in a router:
Is entry in LSDB? Sequence No. same? End No No No Yes Yes Yes LSU/LSA Ignore Add to LSDB Send ACK Flood LSA Run SPF Is sequence number higher than in LSDB? Send LSU back with newer information
Virtual links and OSPF:
Designed for non-contiguous areas
Overcomes the requirement that all areas directly connect to Area 0
Not a good permanent fix to a problem
OSPF — Defining Virtual Links Area 1 Area 0 Area 4 RID 126.96.36.199 RID 188.8.131.52 Virtual link
The objective of the passive interface is to enable an interface to advertise
into an OSPF domain while limiting its adjacencies.
When changing the interface type value to passive, it is advertised into the
OSPF domain as an internal stub network with the following behaviors:
• does not send hello packets into the OSPF domain
• does not receive hello packets from the OSPF domain
• does not form adjacencies in the OSPF domain
Circuitless IP (CLIP) is a virtual (or loopback) interface that is not associated with any physical port. You can use the CLIP interface to provide uninterrupted connectivity to your switch as long as there is an actual path to reach the device .
Open Shortest Path First (OSPF) Section 5 — OSPF Implementation
We can findout what is wrong from trace level 6 3 output : ers8600 :5/trace# level 6 3 ers8600 :5/trace# clear ers8600 :5/trace# info
Passport-8610:5# show ip ospf lsdb lsatype 1 detail Router Link LSA : Area : 0.0.0.0 (0x0) Age : 1011 Opt : true (External Routing Capability) Type : 1 LsId : 184.108.40.206 (0x2dafd800) Rtr : 220.127.116.11 Seq : -2147483640 (0x80000008) Csum : 47803 (0xbabb) Len : 48 ABR : true ASBR : true Vlnk : false (endpoint of active Vlink) #Lnks : 1  Id : 18.104.22.168 (0x8bb16400) Data : 255.255.255.0 (0xffffff00) Type : (conn-to-stub-net)(Id=Subnet-Prefix, Data=Prefix-Len) #Tos : 0 Met : 10
1 To verify that OSPF is enabled on the local router and on the
neighbor router, enter the following CLI command:
show ip ospf info
enter the following NNCLI command:
show ip ospf
Also, from the command output, verify that the router IDs are
different on the local router and the neighbor router.
2 To verify that OSPF is enabled on the local router interface and
the neighbor router interface, enter the following command using
the CLI or NNCLI:
show ip ospf interface
Also, from the command output, verify that the OSPF interfaces
are not configured as passive interfaces.
3 To verify the reachability of the neighbor, enter the following
command using the CLI or NNCLI:
4 To verify the reachability of the neighbor through the
allSPFRouters address, enter the following CLI command (and
see whether the neighbor responds):
5 Verify that the following parameters are configured to the
same values on both interfaces: subnet, hello interval, and
dead interval. To display these parameters, enter the following
command using the CLI or NNCLI:
show ip ospf int-timers
6 Verify that the following parameters are configured to the same
values on both interfaces: area ID, area type (for example, stub
or NSSA). To display these parameters, enter the following
command using the CLI or NNCLI:
show ip ospf area
7 Verify that configured access lists are not affecting OSPF or IP
traffic between the neighbors. To display the ACL configuration,
enter the following command using the CLI or NNCLI:
show filter acl config
Diagnosing OSPF neighbor state problems
At initial startup, routers transmit hello packets in an attempt to find other OSPF routers with which form adjacencies. After the hello packets are received, the routers perform an initialization process, which causes the routers to transition through various states before the adjacency is e stablished .
Step State Description
1 Down : Indicates that a neighbor was configured manually,
but the router did not received any information from
the other router. This state can occur only on NBMA
2 Attempt : On an NBMA interface, this state occurs when the
router attempts to send unicast hellos to any configured
3 Init : The router received a general hello packet (without its
Router ID) from another router.
4 2-Way : The router received a Hello directed to it from another
router. (The hello contains its Router ID.)
5 ExStart : Indicates the start of the Master/Slave election process.
6 Exchange : Indicates the link state database (LSDB) is exchanged
7 Loading : Indicates the processing state of the LSDB for input
into the routing table. The router can request LSA for
missing or corrupt routes.
8 Full : Indicates the normal full adjacency state
Problems with OSPF occur most often during the initial startup, when the
router cannot form adjacencies with other routers and the state is stuck in
the Init or ExStart/Exchange state.
Init state problems
A router can be stuck in Init state and not form an adjacency. There are
several possible causes for this type of problem:
Authentication mismatch or configuration problem
There could be a mismatch in authentication keys or both sides are not
configured for authentication.
To determine if this is causing the problem, issue the trace Level 6 2
command, which allows you to see the OSPF packets that are received:
ERS-8606:5# trace level 6 2
ERS-8606:5# trace screen on
The following example shows the error received when there is an
Ensure that the path is not reachable due to access lists implemented on routers:
Ensure the multicast address of 22.214.171.124 is able to traverse the link.
If multicast traffic is being blocked for some reason, you must to configure the Ethernet Routing Switch 8600 for OSPF nonbroadcast multiaccess area (NBMA), instead of Broadcast.
Although both routers can recognize each other and have moved beyond 2-way, the routers could be stuck in the ExStart/Exchange state. A mismatch in maximum transmission unites (MTU) sizes between the routers usually causes this type of problem. For example, one router could be set for a high MTU size and the other router’s default value is a smaller value. Depending on the size of the LSDB, the router with the smaller value may not be able to process the larger packets and thus be stuck in ExStart/Exchange state. To avoid this problem, ensure that the MTU size
value for both routers match. This problem is usually encountered during interoperations in networks with other vendor devices. Use the trace level 6 2 command to help troubleshoot this type of problem
Incoming OSPF database description (DBD) packets are dropped if their MTU size is greater than 1500 bytes. To allow the Ethernet Routing Switch 8600 to accept OSPF DBD packets with a different MTU size, enable mtu-ignore using the following command:
ERS-8606:5# config ip ospf interface <ipaddr> mtu-ignore
• ipaddr is the IP address of the OSPF interface.
• enable|disable enables or disables the feature.
8600 Feature Matrix
Router ID need to be different from any physical IP’s.
At the ERS 5510, a specific configuration need to be done :
ip ospf op-mode 5510
ERS5500 series and ers 8300 need advanced license to configure OSPF.
The Nortel Ethernet Routing Switch 5000 Series implementation of OSPF only
supports broadcast and passive interfaces. Point-to-point and NBMA interfaces
are not supported.
Important Points at OSPF
Interfaces which do not need to run the routing protocol, should be kept as externals. OSPF Announce Policies must then be applied to import RIP and local routes into the OSPF LSDB.
OSPF Passive interfaces are OSPF internal routes without forming adjacencies. No OSPF hellos are sent.
OSPF route summarization and black hole routes
When you create an OSPF area route summary on an area boundary router (ABR), be aware that the summary route can attract traffic to the ABR that it does not have a specific destination route for. If you have enabled ICMP unreachable message generation on the switch, this may result in a high CPU utilization rate.
To avoid such a scenario, Nortel recommends that you use a black hole static route configuration. The black hole static route is a route (equal to the OSPF summary route) with a next hop of 255.255.255.255. This ensures that all traffic that does not have a specific next hop destination route in the routing table is dropped by the hardware.
- Up to 512 routes (local + static + dynamically learned). The 5510 can support up to 512 routes, although in some instances the 5510 may only be able to scale to 64 routes depending on address distribution/sequence. However, any 5510 configuration supports a minimum of 64 routes, and in most cases will support many more routes (that is, up to 512). Nortel always supports the default route. The 5520 and 5530 also support 512 routes, and testing indicates that more than 512 routes are possible in some configurations, although 512 is the officially supported limit.
1) Regarding the statement "The 5510 can support up to 512 routes, although in some instances the 5510 may only be able to scale to 64 routes depending on address distribution/sequence.", are there any other factors that may limit the number of learned routes to 64.
In a situation like the above network, OSPF (Open Shortest Path First) routes can be summarized to reduce the routing table.
To distribute local attached interfaces into OSPF as a summary on the ERS (Ethernet Routing Switch) 8600 the following steps need to be performed. In this topology ERS 8600 will send the static routes to ERS 5510:
The below processes must be done : - Configuration of the ERS 8600 to be an ASBR (Autonomous System Border Router) - Creation of a policy that matches to the locally attached interfaces and distributes a summary - Configuration of the OSPF redistribution entry To summarize the routes, the local attached interfaces must not run OSPF.
In this example below the 3 local attached interfaces 192.168.4.0/24, 192.168.5.0/24 and 192.168.6.0/24 will be advertised as 192.168.0.0/16 into OSPF.
Configure the VLANs (Virtual LAN) 192.168.4.0,192.168.5.0 and 192.168.6.0 all with mask 24 vlan 4 create byport 1 vlan 4 ports add 2/4 member portmember vlan 4 ip create 192.168.4.173/255.255.255.0 vlan 5 create byport 1 vlan 5 ports add 2/5 member portmember vlan 5 ip create 192.168.5.173/255.255.255.0 vlan 6 create byport 1 vlan 6 ports add 2/6 member portmember vlan 6 ip create 192.168.6.173/255.255.255.0
A prefix list for all 192.168.x.x networks with a mask of 24 Networks with a mask of e.g. 17 or 30 (such as 192.168.7.1/30) will not be covered with this prefix In this case the "mask length from" and "mask length to" would need to be adjusted Ip prefix-list "192.168.0.0_16-24-24" add-prefix 192.168.0.0/16 maskLenFrom 24 maskLenTo 24 This is the prefix to advertise 192.168.0.0/16 as a summary ip prefix-list "192.168.0.0_16-16-16" add-prefix 192.168.0.0/16 maskLenFrom 16 maskLenTo 16 Create a policy ip route-policy "thePolicy" seq 10 create ip route-policy "thePolicy" seq 10 enable ip route-policy "thePolicy" seq 10 match-network "192.168.0.0_16-24-24" ip route-policy "thePolicy" seq 10 set-injectlist "192.168.0.0_16-16-16" General OSPF Config ip ospf admin-state enable The router needs to be ASBR ip ospf as-boundary-router enable ip ospf enable The redistribution policy ip ospf ip ospf redistribute direct metric 10 ip ospf redistribute direct route-policy "thePolicy" ip ospf redistribute direct enable
Before the summarization ip routes for 192.168.4.0, 192.168.5.0, 192.168.6.0 are seen as separately as below: 5510-24T#show ip route =============================================================================== Ip Route =============================================================================== DST MASK NEXT COST VLAN PORT PROT TYPE PRF ------------------------------------------------------------------------------- 0.0.0.0 0.0.0.0 126.96.36.199 10 1 T#1 S IB 5 10.10.10.0 255.255.255.0 10.10.10.53 1 10 ---- C DB 0 188.8.131.52 255.255.255.0 184.108.40.206 1 1 ---- C DB 0 192.168.4.0 255.255.255.0 10.10.10.173 20 10 10 O IB 20 192.168.5.0 255.255.255.0 10.10.10.173 20 10 10 O IB 20 192.168.6.0 255.255.255.0 10.10.10.173 20 10 10 O IB 20 Total Routes: 6 ------------------------------------------------------------------------------- TYPE Legend: I=Indirect Route, D=Direct Route, A=Alternative Route, B=Best Route, E=Ecmp Rou te, U=Unresolved Route, N=Not in HW
after route summarization routing table will be as below all the 192.168.4.0, 192.168.5.0, 192.168.6.0 routes will be seen in 192.168.0.0
WorkAround : Configure ip igmp mrouter between the ospf vlan.
5.1 Load Known Limitations :
Q01832726 : In a SuperMezz R mode HA-CPU system configured with a dead interval of 3 seconds, when the Master is removed, OSPF neighborship is lost for interfaces configured with low timers (for example, 1 s Hello and 3 s Dead Interval). If failover is triggered by soft-resetting the Master CPU, or the dead interval is 10 s, this issue does not occur.
Workaround: Remove the Master CPU during a maintenance window or other low-traffic periods. Or, increase the dead-interval to 10 s.
Q01735063 : When the Link Aggregation Control Protocol (LACP) adds a new port to a link aggregation group (LAG), it brings all the ports of the LAG down, which brings the entire interface down. As a result, the multilink trunk is deleted and the VLAN interface is deleted. This causes OSPF to go down.
Q02008788 : In a square SMLT environment, if OSPF is disabled and re - enabled while the IST is down, the OSPF adjacency to one of the non-IST peer boxes may show ExStart state for 5 to 8 minutes. The condition does clear itself in that time frame, and will go to full adjacency.
HA Feature with OSPF
HA-CPU for Layer 3 redundancy avoids disruption of network traffic when a
master CPU that is running OSPF fails over. It maintains an exact copy of
the OSPF instance of the master CPU on the HA-CPU. When the HA-CPU
initializes, all OSPF information on the master CPU is Table Synchronized
and all OSPF events are Event Synchronized to the HA-CPU. When a
master CPU failover occurs, the OSPF instance on HA-CPU resumes
without affecting router traffic and OSPF neighbors.
During HA-CPU to master CPU transition, it can take up to 3 seconds for the
new master CPU to transmit OSPF packets. Therefore, Nortel recommends
router dead intervals of 5 seconds or higher. (this value is for 8692SF)
OSPF MTU Size Problem Network AB Down Two way received Init Down Init Hello received Two way received Hello received ExStart ExStart Negotioation done Negotioation done Exchange Exchange Router A Router B Neighbor State Neighbor State (Packet too large, dropped) Sequence number mismatch ExStart ExStart Sequence number mismatch (Timeout expired) Hello (DR = B, seen = 0) Hello(DR = 0, seen = 0) Hello (DR = B, seen = A) Hello(DR = B, seen = B) Database Descr. (Seq = Y , Init, Master) Database Descr. (Seq = X , Init, Master) DD (Seq = Y , More, Slave) DD (Seq = Y+1 , Master) Retransmitted DD (Seq = Y , More, Slave) Database Descr. (Seq = Z , Init , Master)
Global OSPF Parameters
TrapEnable - Indicates whether or not traps relating to the Spanning. Tree Protocol should be sent for this STG.
AutoVirtLinkEnable - Enables or disables automatic creation of virtual links.
SpfHoldDownTime - Allows the user to change the OSPF Hold Down timer value (3 to 60 seconds).
LastSpfRun - Indicates the time (SysUpTime) since the last SPF calculated by OSPF.
SPF Run - Allows you to initiate a new SPF run to update the routing table. This feature can be used when you need to immediately restore a deleted OSPF-learned route. It can also be used as a debug mechanism when the routing table’s entries and the link-state database are out of sync.
· Enable - Enables (true) or disables (false) OSPF on the port.
· HelloInterval - The length of time, in seconds, between the Hello
packets that the router sends on the interface. This value must be the
same for all routers attached to a common network.
· RtrDeadInterval - The number of seconds that a router’s Hello packets
have not been seen before its neighbors declare the router down. This
should be some multiple of the Hello interval. This value must be the
same for all routers attached to a common network.
· DesigRtrPriority - The priority of this interface. In multi-access
networks, this field is used in the designated router election algorithm.
The value 0 signifies that the router is not eligible to become the
designated router on this particular network. In the event of a tie in this
value, routers will use their router ID as a tiebreaker. The router with
the highest ID wins.
· Metric - The metric of using this type of service on this interface. The
default value of the TOS 0 Metric is 10^8 / ifSpeed. The value FFFF is
distinguished to mean “no route via this TOS.”
· AuthKey - The Authentication Key. If the area’s authorization type is
simplePassword, and the key length is shorter than 8 octets, the agent
will left-adjust and zero-fill to 8 octets. When read, ospfIfAuthKey
always returns an octet string of length zero. The key may be entered
as ASCII text.
· AreaID - The identification number for the area, typically formatted as
an IP address.
· IfType - When you enable an OSPF interface, you designate it as a
broadcast (active), non-broadcast multiaccess (NBMA) or passive
interface. When an OSPF interface is enabled, you cannot change its
interface type. You must first disable the interface. You can then
change its type and re-enable it. If it is an NMBA interface, you must
also first delete its manually configured neighbors.
· PollInterval - Length of time, in seconds, between hello packets sent to
an inactive OSPF router.
Open Shortest Path First (OSPF) Section 6 — OSPF Implementation Lab workout