Re: Addendum:
- From: Vincent C Jones <vcjones@xxxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 14 Mar 2006 11:15:24 -0500
On Mon, 13 Mar 2006 11:15:14 -0800, Merv wrote:
Packets generated on a router usually use the IP address oof the interface
"closest" to the destination (i.e the interface out of which the packet
will be routed
Generally speaking, unless explicitly overridden, packets originating from
a Cisco router will use as a source address the primary address of the
interface expected to be the interface used to reach the destination. This
results in some interesting source addresses at times...two specific cases
which I've seen in the wild:
1 - The primary IP on an interface with secondary IP's defined will be
used to send packets to a destination on a secondary subnetwork. If the
destination does not have an appropriate default gateway, you can ping the
router's secondary IP from the destination system, but can't ping the
destination system from the router.
2 - The interface actually used to send the packet is not the interface
assumed when assigning the source IP address. Fairly common for syslog
messages about links going up and down. The source IP may be down by
the time the packet is sent.
--
Vincent C Jones, Consultant Expert advice and a helping hand
Networking Unlimited, Inc. for those who want to manage and
Tenafly, NJ Phone: 201 568-7810 control their networking destiny
http://www.networkingunlimited.com
.
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