Tcpdump output example

[banerjee.152]

I am using the command sudo tcpdump -n -i br-lan -e 'arp or icmp' in the openwrt platform to get to see the packets.

d1 and d2 are connected to a router r1.
192.168.1.102 d1
192.168.1.193 d2
192.168.1.1 r1
I am pinging d2 from d1 and checking the tcpdump at the router.

Pinging is working fine and i get to see the tcpdumps.
However some of the outputs are as follows:

 18:48:06.196331 f4:f2:6d:6d:1c:80 > 7c:76:35:d5:be:a7, ethertype IPv4 (0x0800), length 94: 192.168.1.1     > 192.168.1.193: ICMP net 192.168.0.11 unreachable, length 60
18:48:06.447733 f4:f2:6d:6d:1c:80 > 7c:76:35:d5:be:a7, ethertype IPv4 (0x0800), length 94: 192.168.1.1 >   192.168.1.193: ICMP net 192.168.0.11 unreachable, length 60

In my room there is another router R2 connected with no devices. r2- 192.168.0.11

Can anyone explain the 2 lines of output.

[lleachii]

@banerjee.152

In my room there is another router R2 connected with no devices. r2- 192.168.0.11

Please confirm that when you say "connected" - that you're actually referring to a wireless or wired connection between R1 and R2. As the devices in your previous thread lacked a true connection between R1 and R2.

@banerjee.152

Can anyone explain the 2 lines of output.

Yes, Line 1 and 2 state that: the device 192.168.1.1 is informing device 192.168.1.193 - that 192.168.0.11 is not reachable via 192.168.1.1. It used an ICMP Packet Type 3-0 (Destination Network Unreachable) message.

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(Also, moving thread to Installing and Using OpenWrt.)

[jeff]

@banerjee.152

Can anyone explain the 2 lines of output.

Yes, going on your past threads, you're trying to forge the ARP tables for some as-of-yet unexplained reason in an as-of-yet undefined topology. The ICMP packets you're seeing are saying that the combination of your forged ARP tables and routing information is not valid for delivery of the packet.

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