Cisco Systems OL-16066-01 appendix Eguide09186a00804247fc.html, Selectors, page F-593

Appendix K Router Platform User Interface Reference

		Advanced Interface Settings Page
Table K-13	Advanced Interface Settings Dialog Box (Continued)
TCP Maximum		The maximum segment size (MSS) of TCP SYN packets that pass through
Segment Size		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/products/sw/iosswrel/ps1839/products_featur
		e_guide09186a00804247fc.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 network/host objects, or click Select to display an Object
		Selectors, page F-593.
		If the network you want is not listed, click the Create button in the selector
		to display the Network/Host Dialog Box, page F-477. From here, you can
		define a network/host 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 15-29.

	User Guide for Cisco Security Manager 3.2
OL-16066-01		K-29