IGMP Sniffer Trace
IP: Protocol = 2 (IGMP)
IP: Header checksum = 8455 (correct)
IP: Source address = [10.1.3.5]
IP: Destination address = [239.1.1.1]
IP: No options
IP:
IGMP: ----- IGMP header -----
IGMP:
IGMP: Version = 1
IGMP: Type = 2 (Ver1 Membership Report) IGMP: Unused
= 0x00
IGMP: Checksum = AC99 (correct)
IGMP: Group Address = [239.1.1.1]
IGMP:
IP: Protocol = 2 (IGMP)
!Protocol is IGMP
IP: Header checksum = 8455 (correct)
IGMPv2 has additional functionality defined by the following
IGMP packet types and is currently deployed in today's networks:
-
Query election process— All
routers on the segment send query messages to all hosts, 224.0.0.1. The router
with the lowest IP address wins and becomes the query router. Re-election
process starts after 250 seconds if the query router is not heard from.
-
Maximum Response Time field—
This field tweaks the report suppression mechanism (default is 10 seconds). The
purpose of this field is to reduce burstiness, especially on segments with a lot
of multicast receivers. In large segments, it is desirable to tune this value
higher to prevent multiple hosts sending membership reports.
-
Group-specific query message—
After the query router has received a leave group message, the router sends a
group-specific query message to ensure no other hosts require the multicast
flow. The maximum response time field for a group-specific query message is 1
second to keep the latency short. The other query message is a general
membership query message also found in IGMPv1.
-
Leave group messages— The host
sends a leave group message to all routers 224.0.0.2 that it is leaving a
specific multicast group. The query router sends back a group-specific query
message to ensure no other hosts are part of the multicast group. It does this
twice for a total of 2 seconds and then it stops sending that specific multicast
flow down to the segment.
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