source IP of a PING and Traceroute

Unanswered Question
May 7th, 2008
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When I have users ping or traceroute to a specific host...they can do it fine


When I try and ping or trace from

their router....i get stopped along the path.



When I do an extended ping and trace specifying the ip address of a particulre interface from the router-I have success


However, when i specify another source

interface-I get stopped along the path.


and when I ping and trace from my desktop..i have success..


What could be the reason for this?

ACL....Firewall rules?


It doenst really make sense to me, that I able to ping and trace from my desktop

and from the router when i specify a

soure address......but not when i run

a standard ping or trace


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bvsnarayana03 Wed, 05/07/2008 - 10:14
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when you ping from a router, the source of the pkt is the interface IP address from which the pkt is leaving. Hosts may not be knowing the route to reach the WAN ip address.



lamav Wed, 05/07/2008 - 12:21
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As pointed out, packets originating from a router will take on a source IP address of the interface from which it exits, unless you specify the source address.


So, the answer to whether an ACL or FW rule can be causing the lack of reachibility is yes. It could be a result of filtering. A filter may deny traffic being sourced from your exit interface


And, as also pointed out, a lack of routing information for the source network can also prevent reachability. The destination network may not have a route back to the exit inetrface's network.


HTH


Victor


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