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59-17
User Guide for Cisco Security Manager 4.4
OL-28826-01
Chapter 59 Configuring Router Interfaces
Advanced Interface Settings Page
Load Interval The length of time, in seconds, used to calculate the average load on the
interface. Valid values range from 30 to 600 seconds, in multiples of 30
seconds. The default is 300 seconds (5 minutes). Load interval is not
supported on subinterfaces.
Modify the default to shorten the length of time over which load
averages are computed. You can do this if you want load computations
to be more reactive to short bursts of traffic.
Load data is gathered every 5 seconds. This data is used to compute
load statistics, including input/output rate in bits and packets per
second, load, and reliability. Load data is computed using a
weighted-average calculation in which recent load data has more
weight in the computation than older load data.
Tip You can use this option to increase or decrease the likelihood of
activating a backup interface; for example, a backup dial
interface may be triggered by a sudden spike in the load on an
active interface.
TCP Maximum Segment
Size
The maximum segment size (MSS) of TCP SYN packets that pass
through this interface. Valid values range from 500 to 1460 bytes. If you
do not specify a value, the MSS is determined by the originating host.
This option helps prevent TCP sessions from being dropped as they
pass through the router. Use this option when the ICMP messages that
perform auto-negotiation of TCP frame size are blocked (for example,
by a firewall). We highly recommend using this option on the tunnel
interfaces of DMVPN networks.
For more information, see TCP MSS Adjustment at this URL:
http://www.cisco.com/en/US/docs/ios/12_2t/12_2t4/feature/guide/ft_a
dmss.html
Note Typically, the optimum MSS is 1452 bytes. This value plus the
20-byte IP header, the 20-byte TCP header, and the 8-byte
PPPoE header add up to a 1500-byte packet that matches the
MTU size for the Ethernet link.
Helper Addresses The helper addresses that are used to forward User Datagram Protocol
(UDP) broadcasts that are received on this interface. Enter one or more
addresses or the names of the network/host objects, or click Select to
select an object from a list or to create a new object.
By default, routers do not forward broadcasts outside of their subnet.
Helper addresses provide a solution by enabling the router to forward
certain types of UDP broadcasts as a unicast to an address on the
destination subnet. For more information, see Understanding Helper
Addresses, page 59-14.
Table 59-6 Advanced Interface Settings Dialog Box (Continued)
Element Description