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New Member

EIGRP : CR mode

Hi,

I had a doubt :

When

- router A sends a multicast to router X and Y,

- receives an ack from X

- but none from Y

=> which router will enter CR mode, when the multicast flow timer expires : X or Y ?

I have searched extensively on cisco.com but found nothing.

Thanks,

Navid

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: EIGRP : CR mode

Hi Navid,

I don't know of any good place to point you to, but I can explain it here. Assume you have three routers on a broadcast segment, A, B, and C.

-- A sends out some reliable packet (it could be an update, query, etc--anything reliable).

-- B acknowledges the packet, but C doesn't.

-- A's retransmission timer counts, and then expires (this timer is actually bound up with the multicast flow timer and the RTO, but I won't confuse the issue with all the relationships there).

-- A will then send out a hello with the CR (conditional receive) bit set, and a list of neighbors that should not pay attention to future multicast packets. C would be on this list, since we are unicasting to C.

-- A will now begin unicasting missed packets to C. If new updates are queued for transmission on the link, A will multicast these to the other routers on the link (B, in this case). A will also unicast these packets to C, waiting for C to ack each one.

-- When A has received an ack for all outstanding routing information queued for transmission from C, it will send out a new hello with the CR bit set, and an empty list of neighbors that should ignore multicast from A. This clears the CR mode.

HTH,Please rate if it does.

-amit singh

2 REPLIES
Cisco Employee

Re: EIGRP : CR mode

Hi Navid,

I don't know of any good place to point you to, but I can explain it here. Assume you have three routers on a broadcast segment, A, B, and C.

-- A sends out some reliable packet (it could be an update, query, etc--anything reliable).

-- B acknowledges the packet, but C doesn't.

-- A's retransmission timer counts, and then expires (this timer is actually bound up with the multicast flow timer and the RTO, but I won't confuse the issue with all the relationships there).

-- A will then send out a hello with the CR (conditional receive) bit set, and a list of neighbors that should not pay attention to future multicast packets. C would be on this list, since we are unicasting to C.

-- A will now begin unicasting missed packets to C. If new updates are queued for transmission on the link, A will multicast these to the other routers on the link (B, in this case). A will also unicast these packets to C, waiting for C to ack each one.

-- When A has received an ack for all outstanding routing information queued for transmission from C, it will send out a new hello with the CR bit set, and an empty list of neighbors that should ignore multicast from A. This clears the CR mode.

HTH,Please rate if it does.

-amit singh

New Member

Re: EIGRP : CR mode

Great !

Thanks.

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