Configuring IP Router Parameters
36 7705 SAR OS Router Configuration Guide
These options are copied into the DHCP reply message, but if the same option is defined
several times, the following order of priority is used:
1. subnet options
2. pool options
3. options from the DHCP client request
A local DHCP server must be bound to a specified interface by referencing the server from
that interface. The DHCP server will then be addressable by the IP address of that interface.
A normal interface or a loopback interface can be used.
A DHCP client is defined by the MAC address and the circuit identifier. This implies that for
a certain combination of MAC and circuit identifier, only one IP address can be returned; if
more than one request is made, the same address will be returned.
ICMP and ICMPv6
Internet Control Message Protocol (ICMP) is part of the Internet Protocol Suite as defined in
RFC 792, Internet Control Message Protocol, for IPv4 and RFC 4443, Internet Control
Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification. The
neighbor discovery capability of ICMPv6 is specified in RFC 4861, Neighbor Discovery for
IP Version 6 (IPv6).
ICMP messages are typically generated in response to errors in IP datagrams or for diagnostic
or routing purposes. The ICMP ping utility for IPv4 and IPv6 and the ICMP traceroute utility
for IPv4 are described in the 7705 SAR OS OAM and Diagnostics Guide, “ICMP
Diagnostics”.
The 7705 SAR supports the ICMP capabilities described in Table 3.
Table 3: ICMP Capabilities for IPv4
ICMP Message Description
Address mask reply Used to reply to an address mask request with an
appropriate subnet mask
Time exceeded (TTL expired) Generated by a router to inform the source of a
packet that was discarded due to the time to live
(TTL) field reaching zero
Used by the traceroute utility to obtain a list of
hosts that the packets traversed from source to
destination
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