Extreme Networks ExtremeWare 7.5, Command Reference Manual

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1584 ExtremeWare 7.5 Command Reference Guide
IP Unicast Commands
A static route must be associated with a valid IP subnet. An IP subnet is associated with a single VLAN
by its IP address and subnet mask. If the VLAN is subsequently deleted, the static route entries using
that subnet must be deleted manually.
When there are multiple, conflicting choices of a route to a particular destination, the router picks the
route with the longest matching network mask. If these are still equal, the router picks the route using
the following criteria (in the order specified):
• Directly attached network interfaces
• ICMP redirects
• Static routes
• Directly attached network interfaces that are not active
If you define multiple default routes, the route that has the lowest metric is used. If there are multiple
default routes that have the same lowest metric, the system picks one of the routes.
You can also configure blackhole routes—traffic to these destinations is silently dropped.
Internet Control Message Protocol (ICMP) is used to transmit information needed to control IP traffic. It
is used mainly to provide information about routes to destination addresses. ICMP redirect messages
inform hosts about more accurate routes to other systems, whereas ICMP unreachable messages indicate
problems with a route.
Additionally, ICMP can cause TCP connection to terminate gracefully if the route becomes unavailable.
After IP unicast routing has been configured, you can configure the switch to forward Dynamic Host
Configuration Protocol (DHCP) or BOOTP requests coming from clients on subnets being service by the
switch and going to hosts on different subnets. This feature can be used in various applications,
including DHCP services between Windows NT servers and clients running Windows 95.
UDP-forwarding is a flexible and generalized routing utility for handling the directed forwarding of
broadcast UDP packets. UDP-forwarding allows applications, such as multiple DHCP relay services
from differing sets of VLANs, to be directed to different DHCP servers. The following rules apply to
UDP broadcast packets handled by this feature:
•
If the UDP profile includes BOOTP or DHCP, the packet is handled according to guidelines in RFC
1542.
• If the UDP profile includes other types of traffic, these packets have the IP destination address
modified as configured, and changes are made to the IP and UDP checksums and decrements to the
TTL field, as appropriate.
If the UDP-forwarding is used for BOOTP or DHCP forwarding purposes, do not configure or use the
existing
bootprelay
function. However, if the previous
bootprelay
functions are adequate, you can
continue to use them.
To configure UPD-forwarding, you must first create a UDP-forward destination profile. The profile
describes the types of UDP packets (by port number) that are used and where they are to be forwarded.
You must give the profile a unique name, in the same manner as a VLAN, protocol filter, or Spanning
Tree Domain (STD).
Next, configure a VLAN to make use of the UDP-forwarding profile. As a result, all incoming traffic
from the VLAN that matches the UDP profile is handled as specified in the UDP-forwarding profile.
A maximum of 10 UDP-forwarding profiles can be defined. Each named profile may contain a
maximum of eight “rules” defining the UDP port, and destination IP address or VLAN. A VLAN can