User`s guide

72 XSR User’s Guide
General IP Features Chapter 5
Configuring IP
 If any router on a network segment uses a secondary address, all
other devices on the same segment must also use a secondary address
from the same network or subnet. Inconsistent use of secondary
addresses on a network segment can quickly cause routing loops.
 Configure the primary IP address before any secondary IP addresses
on the same interface. Conversely, before a primary address can be
removed, all secondary IP addresses should be removed.
 You can configure OSPF, RIP or static routes on each primary and
secondary IP address.
 A secondary IP address is configured using the
ip address
<address> <mask> {secondary}
command.
ARP & Secondary IP
For each IP address configured on the interface, including primary and
secondary IP addresses, the corresponding static ARP entry should be
maintained in the static ARP table. Primary and secondary IP addresses on
the same interface share the same MAC address of the interface.
When an ARP request is received, the destination IP address in the ARP
packet will be checked against the primary IP and all secondary IP addresses.
If found, an ARP reply will be sent back with the MAC address of the
interface. When sending an ARP request, the source IP address used in the
ARP packet should be on the same subnet as the destination IP.
ICMP & Secondary IP
When ICMP Echo packets are received by the XSR, the destination IP address
is checked against all configured IP addresses including primary and
secondary addresses. Any ICMP Echo packet addressed to the subnet
broadcast addresses will be dropped without returning a response.
ICMP Echo Replies are generated by swapping the destination and source IP
addresses in the received ICMP Echo packets.
By default, ICMP Echo packets generated by the XSR’s
ping command will be
sourced by the IP address of the outgoing interface which is in the same
subnet as the IP address of the next-hop the ICMP packet should be
forwarded to.