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Help determining network topology given a network trace?

asked 2019-02-16 01:35:50 +0000

Jusb gravatar image

updated 2019-02-16 23:18:20 +0000

Guy Harris gravatar image

Hi folks...

Sorry if this seems like a silly question, but i don't have much experience using wireshark and Packet Tracer. I'm in need of a little help with a project I'm trying to figure out.

The goal here is to examine the wireshark capture, identify information (such as host, hops IP addresses etc) and recreate the topology using Packet tracer.

So to the best of my beginners knowledge, i have tried to recreate the network from what I’ve observed in the capture.

This a trace route from PC # 1 (172.19.100.37) to PC #2 ( 172.16.200.41 )

what I see is three ICMP TTL messages coming from 172.19.xx | 172.18.xx… and 172.17.xxx, so that’s 3 hops. Since PC # 2 has a IP address of 172.16.200.41, I assume there must be one more router which would presumably 172.16.1.1

So I’ve created the topology the best I can ( See the screenshot), but something isn’t making sense. For one, i need to assign an ip the fa0/1 interface on router 1, but i'm having trouble putting that together.

I’ve also done the following to allow communication between routers.

router ospf 1

network 172.0.0.0 0.255.255.255 area 0

*See Screenshot*

Topology

Wireshark

Am i on the right track here? Any suggestions help would be very much appreciated.

Thanks

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answered 2019-02-16 09:40:11 +0000

Jaap gravatar image

Did you notice that the ICMP errors coming from the upstream interface, facing your host #1? After your ICMP request passes that, without expiring the TTL, it goes on to the next network. So the router with interface 172.17.1.1/16 has an interface 172.16.1.1/16 as well. That is the network on which the next interface is the target interface.

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Thank you veeerrry much !!!! I appreciate your time.
I spent forever trying to figure this out . I'm pretty new to this, but i'm working really hard preparing myself to do a cert.

Jusb gravatar imageJusb ( 2019-02-16 20:37:32 +0000 )edit

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Asked: 2019-02-16 01:35:50 +0000

Seen: 53 times

Last updated: Feb 16