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Change source IP address of IP packet

Posted on 2011-09-28
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Last Modified: 2012-05-12
I have a 6500 switch that has an egress interface with a non-routable ip address.

When I use a simple ping then I get no response because the source IP address is the egress interface.

If I do an extended ping and source from any other IP address on the switch the ping works.

How can I change the source address of the packets sent from this router from the egress interface (the default) to the source ip address of the loopback interface or any other interface?

The "logging source-interface Loopback0" does not appear to be changing the source ip address.
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Question by:Dragon0x40
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by:eeRoot
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You can use NAT to translate a non-routed address to an external routed address.  Is this non-routed address part of a network that can be NAT-ed or just a single address?
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by:Dragon0x40
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The address is part of a cloud that is not routable throughout our entire WAN.

We are talking about using policy based routing.

Can policy based routing change the source ip address of the traffic from the egress interface?

I know we tried the "logging source-interface loopback0" and it did not seem to work and still used the egress interface. Does this command change the source ip or just encapsulate the source into the packet?
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by:eeRoot
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PBR will not change the address, but it will forward traffic based on the policy you set.  -- http://www.cisco.com/en/US/docs/ios/12_0/qos/configuration/guide/qcpolicy.html

Also, you may be able to use static routing to direct the traffic
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by:Dragon0x40
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Yes we plan on trying PBR and using the next-hop command but I am not sure if that will work either as won't the source of the packets still be the egress interface ip address?

Why doesn't the  "logging source-interface loopback0" work?

The far end of the WAN can communicate with the ip address of the loopback0 but cannot route to the ip address of the egress interface.

Shouldn't the  "logging source-interface loopback0" change the source ip address and therfore allow routing to happen?
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eeRoot earned 500 total points
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To the best of my knowledge, the "logging source-interface loopback0" only affect syslog messages that originate from the router/switch in question.  And of course, the loopback0 address has to be defined
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by:Dragon0x40
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I believe that we are trying to use the syslog messages that originate from the switch.

We are using the "logging x.x.x.x" command to specify a log server

My understanding is that the  "logging source-interface loopback0" command should change the source ip address of the packets leaving the switch using the standard syslog port of udp 514?

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