Unicast Ip Routing Into A Vpls Service; Arp And Vpls Fib Interactions - Alcatel-Lucent 7210 SAS M Service Manual

Unicast IP Routing into a VPLS Service

The IP interface MTU parameters may be changed at anytime.

ARP and VPLS FIB Interactions

Two address-oriented table entries are used when routing into a VPLS service. On the routing side,
an ARP entry is used to determine the destination MAC address used by an IP next-hop. In the
case where the destination IP address in the routed packet is a host on the local subnet represented
by the VPLS instance, the destination IP address itself is used as the next-hop IP address in the
ARP cache lookup. If the destination IP address is in a remote subnet that is reached by another
router attached to the VPLS service, the routing lookup returns the local IP address on the VPLS
service of the remote router is returned. If the next-hop is not currently in the ARP cache, the
system generates an ARP request to determine the destination MAC address associated with the
next-hop IP address. IP routing to all destination hosts associated with the next-hop IP address
stops until the ARP cache is populated with an entry for the next-hop. The dynamically populated
ARP entries age out according to the ARP aging timer.
NOTE: In 7210 static ARP, entries cannot be used.
The second address table entry that affects VPLS routed packets is the MAC destination lookup in
the VPLS service context. The MAC associated with the ARP table entry for the IP next-hop may
or may not currently be populated in the VPLS Layer 2FIB table. While the destination MAC is
unknown (not populated in the VPLS FIB), the system is flooded with all packets destined to that
MAC (routed or bridged) to all virtual ports within the VPLS service context. Once the MAC is
known (populated in the VPLS FIB), all packets destined to the MAC (routed or bridged) is
targeted to the specific virtual port where the MAC has been learned. As with ARP entries, static
MAC entries may be created in the VPLS FIB. Dynamically learned MAC addresses are allowed
to age out or be flushed from the VPLS FIB while static MAC entries always remain associated
with a specific virtual port. Dynamic MACs may also be relearned on another VPLS virtual port
than the current virtual port in the FIB. In this case, the system automatically moves the MAC FIB
entry to the new VPLS virtual port.
NOTE: In 7210 SAS, whenever a MAC entry is removed from the VPLS FIB (either explicitly by
the user or due to MAC aging or mac-move), ARP entries which match this MAC address is
removed from the ARP cache. Though the VPLS FIB entries are not removed; an ARP entry ages
out and is removed from the ARP cache.
NOTE: If the VPLS FIB limit is reached and we are no longer able to learn new MAC address,
ARP will also not be learnt.
7210 SAS M Services Guide
Virtual Private LAN Services
Page 297