3Com CoreBuilder 2500 User Manual - page 61
Routing with Classical IP over ATM
4-9
ICMP performs these tasks:
■
Tests whether nodes can be reached (
ICMP Echo Request
and
ICMP Echo Reply
)
— A host or gateway sends an ICMP echo request
to a specified destination. If the destination receives the echo request,
it sends an ICMP echo reply to the sender. This process tests whether
the destination is reachable and responding and verifies that the
network’s transport hardware and software are working. The
ping
command is frequently used to invoke this process.
■
Creates more efficient routing (
ICMP Redirect
)
— Often the host
route configuration specifies the minimum possible routing data that
is needed to communicate (for example, the address of a single
router). The host relies on routers to update its routing table. In the
process of routing packets, a router may detect that a host is not using
the best route. The router sends an ICMP redirect to this host,
requesting that the host use a different gateway when it sends
packets to a destination. The host then sends packets to that
destination using the new route.
■
Informs sources that a packet has exceeded its allocated time to
exist within the network (
ICMP Time Exceeded
)
Routing with
Classical IP over
ATM
CoreBuilder Extended Switching software supports classical IP routing
over ATM ARP in an ATM network. The Classical IP over ATM model uses
Logical IP Subnetworks (LISs) to forward packets within the network
environment.
See the CoreBuilder 2500 Operation Guide for detailed information
about the ATM protocol architecture. See the CoreBuilder 2500
Administration Console User Guide for information about how to
configure ATM ports.
About Logical IP
Subnets (LISs)
A
LIS
is a group of IP nodes that belong to the same subnetwork and are
directly connected to a single ATM network. When you add a node to a
LIS through the Administration Console IP interface menu, you define its
IP address, subnet mask, and the address of an ATM ARP server that
supports it.