Cisco router details

1. Date: June 2029.
Today on a cool summer day, I took apart this router. It is a 2008-year Cisco router, model 2851. It was
damaged beyond repair. The router had water damage, extensive. So let's tear apart this thing, and get
some data. I did a bit of digging to see what makes it work. Lets take some pictures and analyze how
“crazy Cisco” did routers in 2008.
**** UPDATED, I found a 2911 router that I could also surplus and analyze. There is a six (6) year
difference in technology going from 2008 to 2014 and the differences are quite dramatic when
comparing the two router boards. The year 2008 was profound and the 2851 router board is simply
packed with every major vendor of chip!!! It’s a massive jumble of parts. There really are at least ten
different manufacturers of chips on the 2851. Talk about a lot of vendors to keep track of!! Let's go
through some of the massive amount of chips on this old router, then we will compare with a bit of a
newer router, the 2911.
************************************************************
Beginning of the 2851 photos and details ->
This box has a rm5231 CPU from Pmc- Sierra. This company in 2023 is owned by Microsemi.
RM5231 pdf, RM5231 Description, RM5231 Datasheet, RM5231 view ::: ALLDATASHEET :::more

2. PMC is now Microsemi , here is a link. Microsemi | lSemiconductor & System Solutions | Power
Matters
There is a 7855pp6 hifn security processor chip in this router also. Perhap for ssh/ssl/vpn?
This router is chip heavy and has some serious silicon. Lets go through some of the other chips.
In the last section, I would like to go into the functions and details of the network (Ethernet Gigabit)
chips.
But first,
Photos of the chips:
This is the PMC cpu chip and the security
processor from HIFN. I think this daughter board is all for Vpn? It has a CPU, dedicated security
processor, ram and such. A flash memory chip is below this daughter board.

3. Two (2) of these Cisco chips from Korea run
something. I guess they are interface for the cisco expansion cards that go in the back? For this chip,
nothing can be found on what they do. . . perhaps central IOS of the router runs on these? Nothing can
be found on the quick internet search. Any cisco employees know? If they are for IOS, then umm, But
why two (2) chips ?? Maybe because of the two expansion slots? Notice the ”FULL JTAG” test pads.
Usually these are for enabling JTAG testing modes.

4. Here you see the marvel CPU chip
mv96340. Does this cpu run the IOS of the router? very possible. But. . .
Or does the PMC chip? The PMC chip is also a CPU!!! How many CPU does this router have! Wow.
Three (3) CPUs I have counted so far! Some details on this CPU:
RM7065C | Microchip Technology

5. A Safenet security processor chip is tucked
underneath one of the Cisco chips. Another security function but unsure what for, perhaps this board
needed it for basic ssh connections? Mystery.
A daughter card has a serial to parallel chip from NXP and also a flash memory. Perhaps for storing
some settings for the router that are not stored on the compact flash memory?

6. Now on to the network connections, powered by Broadcom!! Unlike most Broadcom chips, these have
a decent amount of information on the internet about what they do.
This is only a two (2) port, gigabit router.
So each of these Broadcom BCM5421KQM chips support one of the gigabit interfaces. Now in 2023 you
will have one chip that supports 8 separte ethernet physical ports. Miniaturization of components and
functions into a plethora of units, all on one chip, is now common. For in 2008, not so much.
Now in 2008, Broadcom showed a bit about what these chips do. There is a decent functional
schematic of how gigabit ethernet works. I will reference it later. THe 824-m0060r are transformers
that connect the ethernet cable to the broadcom chips.
To me, a network card, or ethernet port, has a definition in my head. To me, the definition is something
like this. A network card, or ethernet port, is used to communicate digital information over distances
separated by two or four pairs of twisted cable. It does this by transmitting electromagnetic analog
signals and receiving analog signals and decoding them. A network card also provides AC and DC
isolation from the cable and cable faults. Ethernet ports can operate over a variety of distances by using
automatic sensing of the signal levels and using appropriate amplifiers to receive the signal. The
ethernet port will sense voltage pulses on the cable and can automatically change the speed of the
communication signal to match the end device. Ethernet can effectively change the parameters of the
communications, based on the far end host. Ethernet ports are commonly called “Gigabit ethernet” for

7. the ports that can communicate at 1 billion bits per second. Note that, gigabit ethernet requires four (4)
pairs of twisted pair cable.
One way to help you understand ethernet is to read the patents. For a deep understanding of the
network card, try reading some of the patents. This patent goes into the adjustable amplifiers that
receive the network signal. This patent also has many related patents listed at the end, which cover
many of the electrical and digital inventions that make the modern ethernet work. Enjoy!
https://patents.google.com/patent/US7336131
Read about basics of the modern gigabit ethernet port there. If you read about the NIC using the link,
Godspeed and good for you. Hopefully you will see some of the functions, and the magic of ethernet
will be less magical.
There are tricks that make all this work. Some of the functions that we take for granted are explained in
depth. A few that I did not know about are:
PGA. Programmable gain amplifiers –or- programmable gain attenuators. There are 4db amp steps, and
there are four of them. This shows the variability of the ethernet signal and how the NIC takes that
signal and amplifies it if needed.
The symbol encoder, well I know that sometimes this is used for manchester encoding. Manchester
encoding provides for constant changes in the analog electric signal, even if many zeros or many ones
are being sent. In another document, a phrase called “Baseline wandering” was presented. This again is
the problem of multiple digital zeros or ones being sent over the line. Read about how Manchester
coding works and why:
Baseline wandering in digital transmission | Line coding to eliminate (rfwireless-world.com)
A block diagram of the Broadcom nic chips.

8. Ok, so let's get back to the 2851 router. The router board is just packed with tons of chips that do
different things, all for a router with only two (2) network ports!
Cisco 2851 flash memory and Nxp serial converter. Note even in 2008, we have ”Made in China”.
Unfortunately, much network gear is made in China nowadays.

9. Here is the 2851 field barn router about to
be sent to the surplus yard. RIP Cisco 2851, it was a good time back then in 2008.
Say good bye.

10. ************************************************************
Beginning of the Cisco 2911 photos and details ->
This 2911 router has three (3) gigabit ethernet ports, and was made in the year 2014. Almost a decade
old, this router is not modern. . . but lets us see what we can learn from this box.
Spartan 3. This is a FPGA that was used in this box.
An Xilinx Spartan 3 FPGA. FPGA chips
represent interesting concepts in functionality. Field programmable and the marketing says this is so
much better than a ASIC. Does it really work so much better than an asic? How often do you need to
change the logic gates in a router?

11. Here is the 2911 board as seen after
opening the router.

12. Marvell silicon ethernet chips.

13. More Marvel chips. I think these are for
the three gigabit ports. 88e111 chips. Link below for details.
88E1111 Datasheet (marvell.com)
Almost all Cisco routers that I have ever seen use Foxconn sheet metal housings and brackets. Here is
the foxconn powersupply bracket. All Foxconn use the same quality assurance stamp, see below.

15. Foxcon quality control mark. You see this
on all foxconn metal housings.

16. The 2911 router Cisco
main chip, made in Japan. A new way to pass the heat from the silicon chip to the heat sink, they use an
aluminum metal mesh sandwiched between the CPU and the heat sink. Interesting. . . seems like a good
idea?

17. Cavium networks OCTEON Plus chip.
Cavium was acquired by Marvell Technology Group on July 6, 2018.[7]
I think this is a security vpn processor.
Only two (2) main chips run the board, the Cisco chip and the Octeon chip, it appears to me. Much
simpler board layout, less components for sure. Unsure on how many layers this board is.

18. Say good bye to the
2911 board, it is heading to the trash. Note these boards are difficult to remove, no one ever tries to
repair them. Just get a new router and swap out the config. Take out the flash memory chip and put in
the new router.
This took me a few hours - but I learned a lot. If you don’t know how it works, then how can you
operate it? Take apart and dig into the mystery of your work, and your knowledge will raise your power

19. to a new level! I hope you learned something about networking and routers. Any questions email me
at rod.deluhery AT gmail .com
Copyright 2023 Rod Deluhery
References:
Texas instruments doc on 100 megabit ethernet, a good place to start for understanding basic 100 mb
ethernet. Learn this before going on to learn gigabit ethernet and 2.5 gigabit ethernet.
Click to access snla088a.pdf