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Community Member

Can only ping 1 of 2 SDSL interfaces

Hi,

We have a customer CPE (2611xm) which has 2 x SDSL interfaces, both configured with unique /30 addresses.

The routing table on the CPE is configured as such

ip route 0.0.0.0 0.0.0.0 ATM0/0.38

ip route 0.0.0.0 0.0.0.0 ATM0/1.38

From the directly connected PE, I can ping both interfaces IP addresses successfully. However, from anywhere else, I can only ping one of the interfaces.

If I do a clear ip route * on the CPE, then I can then ping the other interface, but not the one I could successfully ping before.

The CPE is running CEF. Setting CEF to per-packet load sharing cures the problem, however the CPE then grinds to a halt and ping times increases from <20ms to >300ms.

Any advice would be appreciated.

Thanks

Lee

6 REPLIES
Purple

Re: Can only ping 1 of 2 SDSL interfaces

Hi Lee,

I suspect what is happening is that the CPE is replying to the ping which in came in through one interface with a packet that is routed via the other interface and in the process, the source address of the reply packet is different to the destination address of the original request.

Is it possible for you to do a debug ip icmp on the CPE to verify this ?

Regards,

Paresh

Community Member

Re: Can only ping 1 of 2 SDSL interfaces

Hi,

Sorry, I forgot to mention that deb ip icmp shows the CPE replying from the correct interface. Here is output of deb ip icmp on the CPE. Pings to both interface from the same source.

8w6d: ICMP: echo reply sent, src 135.191.226.190, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.226.190, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.226.190, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.226.190, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.239.90, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.239.90, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.239.90, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.239.90, dst 135.191.44.219

8w6d: ICMP: echo reply sent, src 135.191.239.90, dst 135.191.44.219

Purple

Re: Can only ping 1 of 2 SDSL interfaces

Hi again,

So are you saying that the CPE is sending ICMP replies to pings directed to both interface addresses ? Or was your second capture done after you clear the routing table?

Paresh.

Community Member

Re: Can only ping 1 of 2 SDSL interfaces

the CPE sends replies back to the source from both interfaces no matter what.

Its only when I change CEF to per-packet load-sharing that the replies actually get back to the source.

With the default CEF configuration, packets only get back to the source from 1 interface. Even though deb ip icmp shows both interfaces replying correctly from the source icmp echo's.

Hope this clarifies things..

Lee

Purple

Re: Can only ping 1 of 2 SDSL interfaces

Thanks...

Is there any chance you could post the output of some of the 'sh ip cef' commands from the CPE...

Paresh.

Community Member

Re: Can only ping 1 of 2 SDSL interfaces

Here you go. Th 2 atm interfaces are addressed 135.191.226.190 and 135.191.239.90

0.0.0.0/0 attached ATM0/1.38

attached ATM0/0.38

0.0.0.0/32 receive

135.191.23.160/29 attached FastEthernet0/1

135.191.23.160/32 receive

135.191.23.161/32 receive

135.191.23.163/32 135.191.23.163 FastEthernet0/1

135.191.23.164/32 135.191.23.164 FastEthernet0/1

135.191.23.165/32 135.191.23.165 FastEthernet0/1

135.191.23.166/32 135.191.23.166 FastEthernet0/1

135.191.23.167/32 receive

135.191.23.168/29 135.191.23.166 FastEthernet0/1

135.191.23.176/29 135.191.23.166 FastEthernet0/1

135.191.23.184/29 135.191.23.166 FastEthernet0/1

135.191.226.188/30 attached ATM0/0.38

135.191.226.188/32 receive

135.191.226.190/32 receive

135.191.226.191/32 receive

135.191.239.88/30 attached ATM0/1.38

135.191.239.88/32 receive

135.191.239.90/32 receive

135.191.239.91/32 receive

212.1.17.12/30 attached FastEthernet0/0

212.1.17.12/32 receive

212.1.17.13/32 receive

212.1.17.14/32 212.1.17.14 FastEthernet0/0

212.1.17.15/32 receive

224.0.0.0/4 drop

224.0.0.0/24 receive

255.255.255.255/32 receive

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