Routing Loops

[joekurian123]

Hello,

I am facing some problem with our network, it seems like there is some routing loop.

When I traceroute from my PC(10.51.40.12) to our remote location switch(10.50.8.250) I am getting the follwing output:

C:\>tracert 10.50.8.250

Tracing route to 10.50.8.250 over a maximum of 30 hops

1 <1 ms <1 ms <1 ms 10.51.40.250

2 <1 ms <1 ms <1 ms 10.51.90.254

3 1 ms 1 ms 1 ms 10.51.101.254

4 2 ms 2 ms 2 ms 10.2.110.117

5 2 ms 2 ms 2 ms 10.2.110.57

6 4 ms 4 ms 4 ms 10.2.111.122

7 4 ms 4 ms 4 ms 10.50.8.250

Trace complete

Alternatively when I give the Traceroute from the remote side, I get the

Switch#traceroute 10.51.40.9

Type escape sequence to abort.

Tracing the route to 10.51.40.9

1 10.50.8.201 0 msec 0 msec 0 msec

2 10.2.111.121 4 msec 0 msec 4 msec

3 10.2.110.58 4 msec 0 msec 4 msec

4 10.2.110.118 4 msec 4 msec 4 msec

5 10.51.40.9 4 msec 4 msec 4 msec

6 10.51.40.9 4 msec 4 msec 4 msec

7 10.51.40.9 4 msec 4 msec 4 msec

What I dont understand is that why is the IP address of my PC showing three times. The number of HOPs seems to be 7 both ways, I checked in the routing table of the routers I cant see any routing loops as well.We are using OSPF as the routing protocol.

Can anybody advise what does the output of this Traceroute indicate, is it normal ?

Thanks

[spremkumar]

Hi

As you have mentioned in your post itself .12 is ur pcs ip then what about .9 .is it belongs to any proxy or f/w ? to which equipment the ip is being assigned.

AFAIK if u have ospf and multiple links with equal cost on them u will get different link address but thts with the same hop number,thats not the case in your trace result.

i feel .121,.57,.117 are the link ips which is connecting your site to the remote network .

hows the network setup out ther ? do u have any PBR or anything in that kinda configured over there ?

regds

[tekha]

In case 10.51.101.254 (10.2.110.118) is a Pix FW, you might get that type of reply.

But only when 10.2.110.118 is the outside address and 10.51.101.254 is the inside, and only when tracing from outside->inside, not when tracing inside->outside.

[joekurian123]

Hi,

Thanks for the reply, sorry .9 is my PC IP address itself its not .12.

As you have mentioned correctly 10.51.101.254 is the inside of PIX and we are getting this when tracing from outside to inside only.But why is it happening like this is the PIX blocking it.

Thanks

[tekha]

Apparently this is normal behaviour for a pix when not blocking traceroute from outside->inside, the pix replaces all replies with the destination address.

I didn’t know this myself until a week or two ago.