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(QCT) (Config)#exit
7.4.
IP Helper
The IP Helper feature provides the ability for a router to forward configured UDP broadcast packets to a
particular IP address. This allows applications to reach servers on non-local subnets. This is possible even when
the application is designed to assume a server is always on a local subnet or when the application uses
broadcast packets to reach the server (with the limited broadcast address 255.255.255.255, or a network
directed broadcast address).
You can configure relay entries globally and on routing interfaces. Each relay entry maps an ingress interface
and destination UDP port number to a single IPv4 address (the helper address). Multiple relay entries may
be configured for the same interface and UDP port, in which case the relay agent relays matching packets to
each server address. Interface configuration takes priority over global configuration. If the destination UDP
port for a packet matches any entry on the ingress interface, the packet is handled according to the
interface configuration. If the packet does not match any entry on the ingress interface, the packet is
handled according to the global IP helper configuration.
You can configure discard relay entries. Discard entries are used to discard packets received on a specific
interface when those packets would otherwise be relayed according to a global relay entry. Discard relay
entries may be configured on interfaces, but are not configured globally.
Additionally, you can configure which UDP ports are forwarded. Certain UDP port numbers can be specified
by name in the CLI, but you can also configure a relay entry with any UDP port number. You may configure
relay entries that do not specify a destination UDP port. The relay agent assumes that these entries match
packets with the UDP destination ports listed in Table 13 (the list of default ports).
Table 7-2: Default Ports – UDP Port Numbers Implied by Wildcard
The system limits the number of relay entries to four times the maximum number of routing interfaces (512
relay entries). There is no limit to the number of relay entries on an individual interface, and no limit to the
number of servers for a given {interface, UDP port} pair.
Certain configurable DHCP relay options do not apply to relay of other protocols. You may optionally set a
maximum hop count or minimum wait time using the
bootpdhcprelay maxhopcount
and
bootpdhcprelay
minwaittime
commands.
The relay agent relays DHCP packets in both directions. It relays broadcast packets from the client to one or
more DHCP servers, and relays packets to the client that the DHCP server unicasts back to the relay agent. For
other protocols, the relay agent only relays broadcast packets from the client to the server. Packets from the
Содержание QuantaMesh QNOS5
Страница 1: ...QuantaMesh Ethernet Switch Configuration Guide QNOS5 NOS Platform ...
Страница 209: ...209 Table 7 8 IPv6 Neighbor Discovery Settings ...
Страница 226: ...226 Table 8 2 L3 Multicast Defaults ...
Страница 254: ...254 Appendix A Term and Acronyms Table 9 5 Terms and Acronyms ...
Страница 255: ...255 Table 9 6 Terms and Acronyms Cont ...
Страница 256: ...256 Table 9 7 Terms and Acronyms Cont ...