Extreme Networks ExtremeWare XOS Guide Manual page 506

IPv4 Unicast Routing
RIP. This section describes the behavior of the Routing Information Protocol (RIP) in an IP multinetting
environment:
RIP does not send any routing information update on the secondary interfaces. However, RIP will
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advertise networks corresponding to secondary interfaces in its routing information packet to the
primary interface.
Any inbound RIP control packets from secondary interfaces are dropped.
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Direct routes corresponding to secondary interfaces can be exported into the RIP domain (by
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enabling export of direct routes), if RIP is not enabled on the container VLAN.
BGP. There are no behavioral changes in the Border Gateway Protocol (BGP) in an IP multinetting
environment. This section describes a set of recommendations for using BGP with IP multinetting:
Be careful of creating a BGP neighbor session with a BGP speaker residing in secondary subnet. This
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situation may lead to routing loops.
All secondary subnets are like stub networks, so you must configure BGP in such a way that the
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BGP next hop becomes reachable using the primary subnet of a VLAN.
When setting the BGP next hop using an inbound or outbound policy, ensure that the next hop is
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reachable from the primary interface.
A BGP static network's reachability can also be resolved from the secondary subnet.
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Secondary interface addresses can be used as the source interface for a BGP neighbor.
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Direct routes corresponding to secondary interfaces can be exported into the BGP domain (by
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enabling export of direct routes).
IGMP Snooping and IGMP
Internet Group Management Protocol (IGMP) snooping and IGMP treat the VLAN as an interface.
Only control packets with a source address belonging to the IP networks configured on that interface
are accepted. IGMP accepts membership information that originates from hosts in both the primary and
secondary subnets. The following describes the changes in behavior of IGMP in an IP multinetting
environment:
A layer 3 VLAN will always use the primary IP address as the source address to send out an IGMP
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query, and querier election is based on the primary IP address of interface. Because the RFC dictates
that there is only one querier per physical segment, the querier may be attached to any of configured
IP interfaces, including secondary interfaces, although this is not a recommended configuration.
For a static IGMP group, the membership report is also sent out using the primary IP address.
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For local multicast groups such as 224.0.0.X, the membership report is sent out using the first IP
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address configured on the interface, which is the primary IP address in ExtremeWare XOS.
The source IP address check is disabled for any IGMP control packets (such as IGMP query and
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IGMP membership report). Source IP address checking for IGMP control packet id disabled for all
VLANs, not just the multinetted VLANs.
Multicast Routing Protocols
For Protocol-Independent Multicast (PIM), the following behavior changes should be noted in a
multinetting environment:
PIM does not peer with any other PIM router on a secondary subnet.
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PIM also processes data packets from the host on secondary subnets.
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ExtremeWare XOS 11.3 Concepts Guide