Data Center LAN Migration Guide - Juniper Networks

The commands presented in this section should highlight the proper VPLS operation as follows:
• Sending to unknown MAC address, VPLS edge router floods to all members of the VPLS.
• Sending to a known MAC address, VPLS edge router maps to an outer and inner label.
Data Center LAN Migration Guide
• Receiving a MAC address, VPLS edge router identifies the sender and maps the MAC address to a label stack in the
MAC address cache.
• VPLS provider edge (PE) router periodically ages out unused entries from the MAC address cache.
Multicast
Looked at simplistically, multicast routing is upside down unicast routing. Multicast routing functionality is focused on
where the packet came from and directs traffic away from its source. When troubleshooting multicast, the following
methodology is recommended:
• Gather information
In one-to-many and many-to-many communications, it is important to have a good understanding of the expected
traffic flow to clearly identify all sources and receivers for a particular multicast group.
• Verify receiver interest by issuing the following commands:
show igmp group displays information about Internet Group Management Protocol (IGMP) group
membership received from the multicast receivers on the LAN interface.
show pim interfaces is used to verify the designated router for that interface or VLAN.
• Verify knowledge of the active source by issuing the following commands:
show multicast route group source-prefix extensive displays the forwarding state (pruned
or forwarding) and the rate for this multicast route.
show pim rps extensive determines if the source designated router has the right rendezvous point (RP) and displays
tunnel interface-related information for register message for encapsulation/de-encapsulation.
• Trace the forwarding state backwards, working your way back towards the source IP and looking for Physical
Interface Module (PIM) problems along the way with the following commands:
show pim neighbors displays information about PIM neighbors.
Show pim join extensive validates outgoing interface list and upstream neighbor and displays source tree
and shared tree (Real-Time Transport Protocol or RTP) state, with join/prune status.
Show multicast route group source-prefix produces extensive checks if traffic is flowing
and has a positive traffic rate.
show multicast rpf Multicast routing uses “reverse path forwarding” check. A router forwards only
multicast packets if received on the upstream interface to the source. Otherwise, the RPF check fails, and the packet is
discarded.
Quality of Service/Class of Service (CoS)
Link congestion in the network can be the root cause of packet drops. The show interfaces queue command provides
CoS queue statistics for all physical interfaces to assist in determining the number of packets dropped due to tail drop,
and the number of packets dropped due to random early detection (RED).
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