Cabletron Systems SmartSwitch Router, User'S Reference Manual

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SmartSwitch Router User Reference Manual 91
Chapter 6: IP Routing Configuration Guide
Configuring IP Helper
You can configure the SSR to forward UDP broadcast packets received on a given interface
to all other interfaces or to a specified IP address. You can specify a UDP port number for
which UDP broadcast packets with that destination port number will be forwarded. By
default, if no UDP port number is specified, the SSR will forward UDP broadcast packets
for the following six services:
• BOOTP/DHCP (port 67 and 68)
• DNS (port 37)
• NetBIOS Name Server (port 137)
• NetBIOS Datagram Server (port 138)
• TACACS Server (port 49)
• Time Service (port 37)
To configure a destination to which UDP packets will be forwarded, enter the following
command in Configure mode:
Configuring Direct Broadcast
You can configure the SSR to forward all directed broadcast traffic from the local subnet to
a specified IP address or all associated IP addresses. This is a more efficient method than
defining only one local interface and remote IP address destination at a time with the
ip-
helper command when you are forwarding traffic from more than one interface in the
local subnet to a remote destination IP address.
To forward all directed broadcast traffic to a specified IP address, enter the following
command in Configure mode:
Configuring Denial of Service (DOS)
By default, the SSR installs flows in the hardware so that packets sent as directed
broadcasts are dropped in hardware, if directed broadcast is not enabled on the interface
where the packet is received. You can disable this feature, causing directed broadcast
Specify local subnet interface,
destination “helper” IP
address, and UDP port
number to forward.
ip helper-address interface
<interface-name>
<helper-address>|
all-interfaces
[ <udp-port#> ]
Forward directed broadcast
traffic.
ip enable directed-broadcast interface
<interface name>
|all