Subject: [pim] Interop with old IGMP version routers

From: "Prashant Jhingran" <[email-masked]>
Date: 22 Apr 2003 14:09:14 -0000

Hi,

Section 4 of RFC 2236 is as follows:
An IGMPv2 router may be placed on a subnet where at least one 
router
on the subnet has not yet been upgraded to IGMPv2. The following
requirements apply:

If any IGMPv1 routers are present, the querier MUST use IGMPv1. 
The use
of IGMPv1 must be administratively configured, as there is no 
reliable
way of dynamically determining whether IGMPv1 routers are present 
on a
network. Implementations MAY provide a way for system 
administrators to
enable the use of IGMPv1 on their routers; in the absence of 
explicit
configuration, the configuration MUST default to IGMPv2.

Section 7.3.1 of RFC 3376:
If a router is not explicitly configured to use IGMPv1 or IGMPv2 
and hears an IGMPv1 Query or IGMPv2 General Query, it SHOULD log a 
warning.  These warnings MUST be rate-limited.

The question is
RFC 2236 clearly specifies that Router MUST use the default 
version. Whereas RFC 3376 does not explicitly specifies about the 
version to be used when it hears a IGMP Query from a lower version 
router.
Can we follow the guidelines of the RFC 2236 and extend it further 
for IGMPv3 (i.e. the configuration MUST default to IGMPv3), or 
shall we downgrade the version  automatically to interop with 
lower version routers ??

Kind Regards,
-Prashant

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