Alcatel-Lucent 7705 Configuration Manual page 22

Configuring IP Router Parameters
There is no limit to the number of MAC addresses per port or per adapter card. If the number
of ARP entries reaches the system limit and a new MAC address that is not already in the
ARP table becomes available, at least one MAC address must be flushed from the ARP table
with the command clear>router>arp.
Dynamic ARP and Static MAC entry
The MAC address of the far end can be learned dynamically or be statically configured.
ARP is the common way to dynamically resolve the MAC address of next-hop IP hosts and
is the primary way to resolve IP-to-MAC associations. ARP packets are sent as soon as a
MAC address resolution is needed for a given IP address.
Static configuration of MAC addresses for next-hop routers is also supported. Static
configuration provides a higher level of security against IP hijacking attacks.
Configurable ARP Retry Timer
A timer is available to configure a shorter retry interval when an ARP request fails. An ARP
request may fail for a number of reasons, such as network connectivity issues. By default, the
7705 SAR waits 5000 ms before retrying an ARP request. The configurable retry timer makes
it possible to shorten the retry interval to between 100 and 30 000 ms.
22
Note:
• Because timeout is built into dynamic ARP, the MAC address of the remote peer needs
to be renewed periodically. The flow of IP traffic resets the timers back to their maximum
values. In the case of LDP ECMP, one link could be used for transporting user MPLS
(pseudowire) traffic while the LDP session could be transported on another equal cost
link. In ECMP for LDP and static LSP cases, it is important to ensure that the remote
MAC address is learned and does not expire. Some of the equal cost links might only
be transporting MPLS traffic, and in the absence of IP traffic, learned MAC addresses
will eventually expire. Configuring static ARP entries or running continuous IP traffic
ensures that the remote MAC address is always known. Running BFD for fast detection
of Layer 2 faults or running any OAM tools with SAA ensures that the learned MAC
addresses do not expire.
• For information on LDPs and static LSPs, refer to the 7705 SAR OS MPLS Guide.
Note: The ARP retry default value of 5000 ms is intended to protect CPU cycles on the
7705 SAR, especially when it has a large number of interfaces. Configuring the ARP retry
timer to a value shorter than the default should be done only on mission-critical links, such
as uplinks or aggregate spoke SDPs transporting mobile traffic; otherwise, the retry interval
should be left at the default value.
7705 SAR OS Router Configuration Guide