From: Chris Lewis \(chrlewis\) (chrlewis@cisco.com)
Date: Mon Jul 18 2005 - 14:26:35 GMT-3
CR is an abbreviation for conditional receive, this mode is best
understood with reference to a number of EIGRP neighbors connected on an
ethernet. Let's say routers A, B, C and D are on one common ethernet
subnet and have formed neighbor relationships with each other. If router
A gains a new subnet to advcertize, it will first attempt to use the
reliable multicast mechanism of EIGRP to distribute that information, to
make most efficient use of network resources. This means it sends the
update to 224.0.0.10. Presume routers B and D acknowledge receipt, but C
does not, what happens?
Router A waits for the multiacst flow timer to expire, then sends a
sequence tlv telling router C not to listen to multicast packets coming
from itself. The routers not listed in this packet enter CR mode and
continue listening to multicast. From now on (until Router C has its
database synchronized) Router A will send multicast packets out with the
conditional receive bit set in the multicast updates, which B and D will
process.
Router A starts sending unicast packets to Router C until router C has
caught up. Once C has caught up, Router A sends a packet to clear CR
mode on B and D. If a router has been cleared from CR mode (or never
received a sequence tlv) and receives a packet with the CR bit set, it
will drop it. If Router C does not respond to the unicast packets, the
neighbor is taken down.
I'm struggling to think of a lab scenario where this would be relevant,
do you have one? It is not something you can manipulate with CLI.
Chris
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Nawaz, Ajaz
Sent: Monday, July 18, 2005 11:33 AM
To: ccielab@groupstudy.com
Subject: EIGRP CR Mode & Non CR Mode ?
Could anyone kindly shed some light on the meaning of eigrp neighbour in
CR MODE ?
And NON CR Mode ?
Tia
Ajaz
-----------------------------------------
Information in this email may be privileged, confidential and is
intended exclusively for the addressee. The views expressed may not be
official policy, but the personal views of the originator. If you have
received it in error, please notify the sender by return e-mail and
delete it from your system. You should not reproduce, distribute, store,
retransmit, use or
disclose its contents to anyone. Please note we reserve the right to
monitor all e-mail communication through our internal and external
networks.
This archive was generated by hypermail 2.1.4 : Sun Sep 04 2005 - 17:00:30 GMT-3