TCP/IPv6 Configuration and Management Manual (G06.24+)

NonStop TCP/IPv6 Protocols and Configuration Files
HP NonStop TCP/IPv6 Configuration and Management Manual—524523-008
D-5
Address Resolution Protocol (ARP)
manually a static default route to the specific IP address of the router. If the router's IP
address changes, the configuration files on the NonStop machine must change also.
With IRDP, there is no need to change any configuration files other than initially
enabling the IRDP feature.
When route hold-down times and advertisement intervals are configured to
approximately 30 seconds on the router, and there is no backup router on the LAN,
IRDP can be used for dead-gateway detection.
When IRDP is enabled on a SUBNET, NonStop TCP/IPv6 processes IRDP messages
from multiple routers on the LAN and switches the default route to the most-preferred
router that is currently advertising a default route. When one router stops advertising,
another can take over. Typically, an application times out while the routers reconfigure
their own routing tables to account for the lost router. If the application can tolerate a
short time out, the TCP connection is maintained. For example, most Telnet
implementations can tolerate time outs up to two minutes.
The NonStop TCP/IPv6 process directly interprets incoming IRDP advertisements and
updates its routing table by adding a default route to the advertising router. Adhering to
RFC 1256, NonStop TCP/IPv6 solicits default routes when new SUBNETs are started.
NonStop TCP/IPv6 also solicits default routes when a multi-hop TCP connection
begins to time-out. A time-out might be because of a router failure.
For more information on the ICMP, refer to RFC 1256 (DDN Protocol Handbook,
Volume 2, DDN Network Information Center, December, 1985, pp. 2-151 through
2-172). Also, refer to the book TCP/IP Illustrated by W. Richard Stevens, Prentice Hall,
1994.
Address Resolution Protocol (ARP)
The Address Resolution Protocol (ARP) dynamically binds a high-level Internet
Address to a low-level physical hardware address. Two machines on a single physical
network must know each other’s physical address to communicate. The ARP’s
address-resolution capability extends across only one physical network and is limited
to networks that support hardware broadcast.
Ethernet (as originally defined by DEC, Intel, and Xerox (DIX)) allows many protocols
to coexist on the same cable. Each protocol uses Ethernet packets (frames) that have
their own type specified in the type field in the Ethernet packet header. The Ethernet
specification requires the 48-bit physical (hardware) addresses that are assigned in
blocks to hardware manufacturers by the Xerox Corporation.
The Internet Protocol (IP) specification requires the 32-bit Internet (IP) addresses that
are assigned by the DDN Network Information Center (NIC) operated by SRI
International in Menlo Park, California.
To use the IP over an Ethernet network (or any other network that uses a different size
address), the two types of addresses must be resolved. The NonStop TCP/IPv6
software uses the Address Resolution Protocol (ARP, RFC 826) to convert 32-bit
Internet (IP) addresses into 48-bit Ethernet addresses. The ARP is a low-level protocol