EIGRP Packet question

Dilbert65

OK here is the play

router 1 losses if seccessor route and has no feasible seccessor.
It sends out a "Query" packet.
Router 2 find a new route and send a "Reply" packet back to router 1.

Now does the "Reply" packet contain the new route? or does router 2 send both a "Reply" and "Update" packet?

Exactly how will router 1 get the new route from router 2?

Thanks.

networker050184

Good question that I didn't really know the answer too so I labbed it up. It looks like the router that responds with the new path information only sends back the Reply and no Update.

Dilbert65

So then how does router 1 get the new route? I tried on my lab as well and got stumped.

networker050184

The information is in the Reply. Check out this Wireshark capture I took out the lab.

Cisco HDLC
Internet Protocol, Src: 10.12.12.2 (10.12.12.2), Dst: 10.12.12.1 (10.12.12.1)
Cisco EIGRP
    Version    = 2
    Opcode = 4 (Reply)
    Checksum   = 0xa60f
    Flags      = 0x00000000
    Sequence   = 105
    Acknowledge  = 55
    Autonomous System  : 1
    IP internal route  =   10.23.23.0/24
        Type = 0x0102 (IP internal route)
        Size = 28 bytes
        Next Hop    = 0.0.0.0
        Delay       = 256000
        Bandwidth   = 25600
        MTU         = 1500
        Hop Count   = 0
        Reliability = 255
        Load        = 1
        Reserved 
        Prefix Length = 24
        Destination = 10.23.23.0

EDIT: Got to love that dynamips serial interface capture! Best way to learn is to check out what the routers are actually sending to each other IMO.

Dilbert65

Thank you very much. That is exactly what I was looking for. Guess I will have to install wireshark for my lab rack in case I run into some other odd ball questions.

Do you have your wireshark hooked into your switch and are you mirroring the port somehow? What I mean is how are you able to get in the middle of the 2 routers to capture that infomation?

networker050184

Dilbert65 wrote: »

Thank you very much. That is exactly what I was looking for. Guess I will have to install wireshark for my lab rack in case I run into some other odd ball questions.

Do you have your wireshark hooked into your switch and are you mirroring the port somehow? What I mean is how are you able to get in the middle of the 2 routers to capture that infomation?

Dynamips can do an inline capture. Its pretty sweet. I'd recommend you check it out if you haven't already. This was actually over a serial link also if you notice the "Cisco HDLC" encapsulation.

Dilbert65

figures I have real equipment. I looked into GNS3 for later studies. Time to google search and come up with something that will work for me.


Thank you again.

networker050184

Dilbert65 wrote: »

figures I have real equipment. I looked into GNS3 for later studies. Time to google search and come up with something that will work for me.


Thank you again.

I don't use GNS3 just dynamips and dynagen. No need fro all that GUI fluff IMO. You can use a SPAN port on a switch for the same thing. You won't be able to sniff serial traffic that way though as its ethernet only. There is the "router IP traffic export capture" feature also you can look into.