As required (but may be disabled) per RFC 1812, Record Route is an option in
the IP header that allows the actual route to be recorded. You are right,
the router will process switch the packet as it must take the packet, open
it up to check to see if the record route option is present and put it's
module address into the forwarding datagram.
Now, the reason behind the nine IP address listing maximum is because the
limited amount of space to store the IP addresses due to the IP header
length - read Richard Stevens, TCP/IP Vol. 1 for more information on how
this works with pointer values increasing by 4 etc.
Here is a simple RR PING from one host to another and you can see the egress
IP of the source, the ingress IP of the destination, the egress IP of the
destination, and finally the ingress IP of the source:
Reply to request 1 (32 ms). Received packet has options
Total option bytes= 40, padded length=40
Record route:
(172.16.0.2)
(172.16.0.3)
(172.16.0.3)
(172.16.0.2) <*>
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
End of list
Nate
-----Original Message-----
From: eric chan [mailto:bigeric123@hotmail.com]
Sent: Tuesday, April 17, 2001 11:41 PM
To: cisco-nsp@puck.nether.net
Subject: [nsp] enquiry on record route
dear all,
do you know the feature of record route in "extend ping" , what
is the concept of this record route? as i know, using record route, you
can see max 9 hops for the packet, and record route bypasses switching
method(such as fast, cef), is that all?
in addition, do you know any document explaining the option in extend
ping ?
thanks
eric
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