EIGRP NXOS vs IOS Differences

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Cisco Nexus 5000 Layer 3 Switching

Objectives
• Describe Layer 3 unicast routing
• EIGRP Fundamentals
• EIGRP Hardware
• NX-OS vs IOS
• Bidirectional Forwarding Detection
• Layer 3 Virtualization
Spot the differences

Layer 3 Unicast Routing Overview

Layer 3 Unicast Routing: Unicast RIB
Unicast RIB maintains routing table on Layer 3 Engine:
• Contains: directly connected routes, static routes, and routes learned
from dynamic unicast routing protocols

EIGRP Fundamentals

• Flexible network design
• Multicast and unicast instead of broadcast  
address
• Support for VLSM and discontiguous subnets
• Manual summarization at any point in the  
internetwork
• Advanced distance vector
• Rapid convergence
• 100% loop-free classless routing
• Easy configuration
• Incremental updates
• Load balancing across equal-  
cost pathways
 
EIGRP Overview

Reliable Transport Protocol
The Reliable Transport Protocol includes the following message types:
• Hello—Used for neighbor discovery and recovery. By default, EIGRP sends a
periodic multicast hello message on the local network at the configured
hello interval. By default, the hello interval is 5 seconds.
• Acknowledgement—Verifies reliable reception of Updates, Queries, and
Replies.
• Updates—Sends to affected neighbors when routing information changes.
Updates include the route destination, address mask, and route metrics
such as delay and bandwidth. The update information is stored in the
EIGRP topology table.
• Queries and Replies—Sent as necessary as part of the Diffusing Update
Algorithm used by EIGRP.

Diffusing Update Algorithm (DUAL)
The Diffusing Update Algorithm (DUAL) calculates the routing information based
on the destination networks in the topology table. The topology table includes
the following information:
• IPv4 address/mask—The network address and network mask for this
destination.
• Successors—The IP address and local interface connection for all feasible
successors or neighbors that advertise a shorter distance to the destination
than the current feasible distance.
• Feasibility distance (FD)—The lowest calculated distance to the destination.
The feasibility distance is the sum of the advertised distance from a
neighbor plus the cost of the link to that neighbor.

Internal Route Metrics
Internal routes are routes that occur between neighbors within the same EIGRP
autonomous system. These routes have the following metrics:
• Next hop—The IP address of the next-hop router.
• Delay—The sum of the delays configured on the interfaces that make up the
route to the destination network. Configured in tens of microseconds.
• Bandwidth—The calculation from the lowest configured bandwidth on an
interface that is part of the route to the destination.
• MTU—The smallest maximum transmission unit value along the route to the
destination.
• Reliability—An indication of the reliability of the links to the destination.
• Load—An indication of how much traffic is on the links to the destination.
By default, EIGRP uses the bandwidth and delay metrics to calculate the
distance to the destination. You can modify the metric weights to include the
other metrics in the calculation.

Composite Metric Calculation

External Route Metrics
External routes are routes that occur between neighbors in different EIGRP
autonomous systems. These routes have the following metrics:
• Next hop—The IP address of the next-hop router.
• Router ID—The router ID of the router that redistributed this route into EIGRP.
• AS Number—The autonomous system number of the destination.
• Protocol ID—A code that represents the routing protocol that learned the
destination route.
• Tag—An arbitrary tag that can be used for route maps.
• Metric—The route metric for this route from the external routing protocol.

EIGRP Hello Packets
• Two routers become neighbors when they see the hello packet of the other
router.
- Hello address = 224.0.0.10
• EIGRP does not form neighbors if K values are mismatched.
• EIGRP does not form neighbors if autonomous system numbers are
mismatched.

EIGRPAdjacency Establishment Conditions
• EIGRP forms neighbors, even if hello time and hold time do not match.
• EIGRP transmits hello packets from the primary address of the interface.
• The neighbor declared dead when no EIGRP packets are received within the
hold interval.

EIGRP Retransmission Policy
• The router keeps a neighbor list and a retransmission list for every neighbor.
• Each reliable packet (update, query, reply) is retransmitted when the packet
is not acknowledged.
• A neighbor relationship is reset when the retry limit (16) for reliable packets is
reached.
• Retransmission occurs each time the RTO is reached.

EIGRP Transport Mechanism
• EIGRP transport has a window size of one  
(stop-and-wait mechanism).
- Each reliable packet needs to be acknowledged before the next
sequenced packet can be sent.
- If one or more peers are slow in acknowledging, all other peers suffer.
• Solution: The nonacknowledged multicast packet is retransmitted as a
unicast to the slow neighbor.

Initial Route Discovery

EIGRP Hardware

Nexus 5500 Layer 3 Licence
• Layer 3 Base license
• Included with daughter card / expansion module purchase
• Installation required
• SVIs, L3 routed ports on non-FEX interfaces, routed ACLs and uRPF
• Static Routing, RIPv2, OSPFv2, EIGRP-stub
• HSRP, VRRP
• IGMP v2/v3, PIMv2
• Maximum 256 non-connected OSPF routes
• Layer 3 Enterprise license
• Layer 3 Base license must be present
• Full EIGRP, BGP
• VRF-Lite

Nexus 5500 Layer 3 Support

!
Nexus 5500 Layer 3 Hardware

NX-OS vs IOS
!
Spot the differences

Important Cisco NX-OS and Cisco IOS Software
Differences
• EIGRP command-line interface (CLI) configuration not available until
you enable the EIGRP feature with the feature eigrp command.
• Only the Internet Protocol (IP) is supported. Cisco IOS Software
supports IP, IPX, and Appletalk.
• The EIGRP instance can consist of 20 characters. Cisco IOS Software
supports numbers 1- 65536.
• Eight equal-cost paths are supported by default; Cisco NX-OS
supports up to sixteen.
• Unequal cost load balancing is not supported.
• Route auto-summarization is disabled by default and cannot be
manually configured.
• Networks and interfaces are added to an EIGRP instance under the
interface configuration mode.

Important Cisco NX-OS and Cisco IOS Software
Differences
• If a router ID is not manually configured, the loopback 0 IP address is
always preferred. If loopback 0 does not exist, Cisco NX-OS selects the
IP address for the first loopback interface in the configuration. If no
loopback interfaces exist, Cisco NX-OS selects the IP address for the
first physical interface in the configuration.
• A default route can be generated with the default-information originate
command under the EIGRP instance, whereas Cisco IOS Software
requires additional CLI commands to achieve similar results.
• When interface authentication is configured, the EIGRP key is encrypted
with Data Encryption Standard 3 (3DES) in the configuration. Cisco IOS
Software requires the service password command.
• The neighbor command under an EIGRP routing instance is not supported
at this time, as it shouldn’t be required for Ethernet network topologies.

Things to be aware of
! ▪! Four EIGRP instances can be configured per virtual device context (VDC).!
! ▪! Numerous Virtual Route Forwarding (VRF) instances can be associated with an
EIGRP instance.!
! ▪! If the feature eigrp command is removed, all relevant EIGRP configuration
information is also removed.!
! ▪! The shutdown command can be used to gracefully disable an EIGRP instance while
retaining the configuration. This feature can also be applied per interface with the ip
eigrp <instance> shutdown command.!
! ▪! An EIGRP instance can be restarted with the restart eigrp <instance> Exec
command.!
! ▪! Graceful restart is enabled by default (It needs to be enabled in order to perform an
ISSU upgrade).!
! ▪! Multiple EIGRP instances can be configured on the same interface.!
! ▪! Secondary IP addresses are advertised by default and cannot be suppressed per
interface.!
! ▪! The show running-config eigrp command displays the current EIGRP
configuration.!
! ▪! EIGRP supports Bidirectional Forwarding Detection (BFD), which can be configured
to reduce network convergence time to less than one second.

Configuration Comparison
Enabling the EIGRP Feature
IOS No ability to enable or disable EIGRP.
NX-OS feature eigrp
Configuring an EIGRP Instance and Router ID
IOS router eigrp 10
eigrp router-id 192.168.1.1
NX-OS router eigrp 10
router-id 192.168.1.1

Associating a Network with an EIGRP Instance
IOS router eigrp 10
network 192.168.10.0
NX-OS interface Ethernet2/1
ip address 192.168.10.1/24
ip router eigrp 10
Configuring a Passive Interface
IOS router eigrp 10
network 192.168.10.0 passive-interface GigabitEthernet2/1
ip address 192.168.10.1/24
ip router eigrp 10
ip passive-interface eigrp 10

Configuring Interface Authentication (MD5)
IOS key chain eigrp-key
key 1 key-string cisco123
 
interface GigabitEthernet2/1
ip address 192.168.10.1 255.255.255.0
ip authentication mode eigrp 10 md5 ip authentication key-
chain eigrp 10 eigrp-key
!NX-OS key chain eigrp-key
key 1 key-string 7 070c285f4d06485744
 
interface Ethernet2/1
ip address 192.168.10.1/24
ip router eigrp 10
ip authentication mode eigrp 10 md5
ip authentication key-chain eigrp 10 eigrp-key

Configuring an EIGRP Distribution List to Filter Routes
IOS ip prefix-list eigrp-10-list seq 5 permit 159.142.1.0/24
 
router eigrp 10 network 192.168.10.0 distribute-list prefix
eigrp-10-list out GigabitEthernet2/1
!
NX-OS ip prefix-list eigrp-10-list seq 5 permit 159.142.1.0/24
 
interface Ethernet2/1
ip address 192.168.10.1/24
ip router eigrp 10
ip distribute-list eigrp 10 prefix-list eigrp-10-list out
!

Configuring Route Summarization
IOS ip interface GigabitEthernet2/1
ip address 192.168.10.1 255.255.255.0
ip summary-address eigrp 10 159.142.0.0 255.255.0.0 5
!
ip address 192.168.10.1/24
ip router eigrp 10
ip summary-address eigrp 10 159.142.0.0/16
!
!

Configuring Route Redistribution (Permit all Static Routes)
IOS router eigrp 10
redistribute static
!
redistribute static route-map static-to-eigrp
 
route-map static-to-eigrp permit 10
!
!

Configuring a VRF Instance for EIGRP Routing
IOS router eigrp 10
address-family ipv4 vrf customer-a autonomous-system 20
!
vrf customer-a
autonomous-system 20

Redistribution in NX-OS
Redistribution works differently in NX-OS
• Redistribution can only be accomplished with a Route-Map
NX-OS will not let you do an uncontrolled redistribution as you can with
IOS. (This is a good thing)
• Redistribution does not include interfaces.
When redistributing between two protocols, we will get two types
information redistributed
1. Route known to that protocol and used in the routing table
2. Prefixes associated with any connected interfaces running the
routing protocol

Redistribution Example - IOS
Redistribution of EIGRP into OSPF
would result in 3 External routes
being learned by R3
1. Subnet A would be learned because
it was a part of the EIGRP Routing
table
2. Subnet B and C would be learned
because they are connected
interfaces running EIGRP
Subnet A
Subnet B
Subnet C
EIGRP
OSPF
Subnet D
R1
R2
R3

Redistribution Example - NX-OS
Redistribution of EIGRP into OSPF
would result in 3 External routes
being learned by R3
1. Subnet A would be learned because
it was a part of the EIGRP Routing
table
!
In order to get all the subnets into
OSPF you will need the redistribute
direct command in addition to the
redistribute EIGRP command
Subnet A
Subnet B
Subnet C
EIGRP
OSPF
Subnet D
R1
R2
R3

Management and Troubleshooting Commands
N5K# show ip eigrp topology detail-links vrf 100
IP-EIGRP Topology Table for AS(1)/ID(31.1.1.1) VRF 100 Codes:
P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status 
P 11.0.15.0/30, 5 successors, FD is 768, serno 603 via
11.0.9.2 (768/320), Ethernet1/16.100 
via 11.0.6.2 (768/320), Ethernet1/13.100 
via 11.0.21.2 (768/320), Ethernet1/1.100 
via 11.0.22.2 (768/320), Ethernet1/2.100 
via 11.0.8.2 (768/320), Ethernet1/15.100 
via 11.0.10.2 (1024/768), port-channel10.100
<...> 
show ip eigrp [<instance>] 
show ip eigrp accounting 
show ip eigrp interfaces [detail] 
show ip eigrp neighbors [detail] 
show ip eigrp route 
show ip eigrp route-map statistics redistribute <protocol>
show ip eigrp topology 
show ip eigrp traffic 
show ip eigrp vrf

ECMP Load-Balancing Hash
• Layer 3 hash
• Layer 3 and 4 hash
• Dest-addr hash
• Dest-addr-port hash
Up to 16 Paths
10.1.1.0

Bidirectional Forwarding Detection

BFD Operation
EIGRP Neighbors
BFD Neighbors
X
10.1.1.0/24
10.1.2.1/24 10.1.2.2/24
10.1.3.0/24

Configuring BFD
• Before enabling BFD, the address-identical IDS check has to be disabled
to allow the switch to accept BFD echo packets:
- BFD echo packets are sent with the local IP address as the source and
destination IP address.
!
!
!
!
!
• Enable BFD globally using the feature bfd command:
- ICMP redirects need to be disabled on any interface that uses BFD.
N5K(config)# feature bfd
Please disable the ICMP redirects on all interfaces
running BFD sessions using the command below
!
'no ip redirects '
N5K(config)# feature bfd  
 
BFD Feature could not be enabled.  
 
Please disable the address-identical IDS check for  
BFD Echo to be operational using the configuration  
command given below in the default VDC.  
 
'no hardware ip verify address identical’

Configuring BFD (Cont.)
After BFD has been enabled globally it has to be enabled for a specific
Layer 3 control protocol:
N5K(config)# router eigrp 1
N5K(config-router)# bfd
N5K(config)# int vlan 10
N5K(config-if)# no ip redirects
N5K(config-if)# hsrp bfd
• The following example enables BFD for all interfaces that participate in
a specific EIGRP process.
• The following example enables BFD for all HSRP groups on an
interface.

Verifying BFD
To verify BFD neighbor status, use the show bfd neighbor command.
N5K# show bfd neighbors details
!
OurAddr NeighAddr LD/RD RH/RS Holdown(mul
t) State Int Vrf
10.1.10.1 10.1.10.2 1107296257/1107296257 Up 4757(3)
Up Vlan10 default
!
Session state is Up and using echo function with 50 ms interval
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 50000 us, MinRxInt: 2000000 us, Multiplier: 3
Received MinRxInt: 2000000 us, Received Multiplier: 3
Holdown (hits): 6000 ms (0), Hello (hits): 2000 ms (1058)
Rx Count: 971, Rx Interval (ms) min/max/avg: 716/23723/1914 last: 1242 ms ago
Tx Count: 1058, Tx Interval (ms) min/max/avg: 1757/1757/1757 last: 181 ms ago
Registered protocols: hsrp_engine
Uptime: 0 days 0 hrs 28 mins 26 secs
Last packet: Version: 1 - Diagnostic: 0
State bit: Up - Demand bit: 0
Poll bit: 0 - Final bit: 0
Multiplier: 3 - Length: 24
My Discr.: 1107296257 - Your Discr.: 1107296257
Min tx interval: 50000 - Min rx interval: 2000000
Min Echo interval: 50000
Hosting LC: 1, Down reason: None, Reason not-hosted: None

Layer 3 Virtualization

Virtual Routing and Forwarding
• VRF virtualizes the IP routing control and data plane functions inside a
router or Layer 3 switch.
• VRFs are used to build Layer 3 VPNs.
• A VRF consists of the following:
- A subset of the router interfaces
- A routing table or RIB
- Associated forwarding data structures or FIB
- Associated routing protocol instances

VRF Configuration
• VRFs can be created in the default VDC or any non-default VDC.
• VRFs in different VDCs are completely independent.
• To configure a VRF, perform the following steps:
- Create the VRF.
- Assign Layer 3 interfaces to the VRF.
!
!
!
!
!
Note: When an interface is assigned to a VRF, any existing Layer 3
configuration is removed.
N5K(config)# vrf context PRODUCTION
N5K(config-vrf)#
!
N5K(config)# interface vlan 10
N5K(config-if)# vrf member PRODUCTION
N5K(config-if)# ip address 10.10.10.1/24

VRF Configuration (Cont.)
Static routes for a VRF are configured in VRF configuration mode.
The following example shows how to configure a static route for a VRF and
verify its presence in the VRF routing table.
N5K(config)# vrf context TEST
N5K(config-vrf)# ip route 10.0.0.0/8 172.16.1.1
N5K(config-vrf)# show ip route vrf TEST
IP Route Table for VRF "TEST"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
!
10.0.0.0/8, ubest/mbest: 1/0
*via 172.16.1.1, Vlan11, [1/0], 00:00:53, static
172.16.1.0/24, ubest/mbest: 1/0, attached
*via 172.16.1.2, Vlan11, [0/0], 00:00:54, direct
172.16.1.2/32, ubest/mbest: 1/0, attached
*via 172.16.1.2, Vlan11, [0/0], 00:00:54, local

To enable a routing process for the VRF, the VRF must be associated with
the routing protocol.
The following example shows how to configure OSPF for a VRF.
N5K(config)# vrf context GUESTS
!
N5K(config)# router ospf 1
N5K(config-router)# vrf GUESTS
N5K(config-router-vrf)#
!
N5K(config-if)# vrf member GUESTS
N5K(config-if)# ip router ospf 1 area 37

The following example shows how to configure EIGRP for a VRF.
!
!
!
!
!
!
!
Note: EIGRP for a VRF inherits the autonomous system indicated in the
process tag, unless a separate autonomous system number is configured
for the VRF.
N5K(config)# vrf context VOICE
!
N5K(config)# router eigrp 1
N5K(config-router)# vrf VOICE
N5K(config-router-vrf)# autonomous-system 200
!
N5K(config-if)# vrf member VOICE
N5K(config-if)# ip router eigrp 1

Thank you.

EIGRP NXOS vs IOS Differences

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