
Browse NETS topics: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z	Search NETS:

The NETS Reserved Address Standard - 4/1/08

This document provides guidelines for the gateway and router addresses defined for each subnet. Having a standard to follow will ease troubleshooting and general network management.

NETS uses Hot Standby Routing Protocol (HSRP) as one way to improve network availability. This protocol provides network redundancy by ensuring that user traffic immediately and transparently recovers from first hop failures in network edge devices or access circuits.

HSRP works by sharing an IP address and a MAC (Layer 2) address with two or more routers, allowing a group of routers to act as a single 'virtual' router. The members of this virtual router group continually exchange status messages. This way, one router can assume the routing responsibility of another, should it go out of commission for either planned or unplanned reasons. Hosts continue to forward IP packets to a consistent IP and MAC address, and the changeover of devices doing the routing is transparent.

For more information on this topic
http://www.networksorcery.com/enp/protocol/hsrp.htm

Some existing subnets use 'grandfathered' addresses, however, new subnets will be created using this standard. Documentation of the defined gateway for specific subnets is found on the vlans and subnets pages.

NETS reserved addresses

For the purposed of routing, NETS reserves the following addresses within a /24 subnet:

128.117.xxx.251 - this is the virtual network address used as the default gateway for use by end devices.
128.117.xxx.252 - reserved for future use
128.117.xxx.253 - primary campus router
128.117.xxx.254 - secondary campus router

If these addresses are not available, NETS will work with the division to determine appropriate settings. The router addresses will then be documented on the vlans and subnets pages.

Other addresses in a subnet with specific functions:

128.117.xxx.0 - network address (all zeros)
128.117.xxx.255 - broadcast address (all ones)
128.117.xxx.208 - 223 is the semi-exposed host range

Router DNS entries

NETS also requests DNS entires for these addresses using this convention:

(campus)router-n(subnetnumber).ucar.edu

These examples are for a subnet on the Mesa

the network 'default gateway' address would be 'mlr-n241.ucar.edu' for 128.117.241.251
the primary router interface would be named the 'a' router 'mlra-n241.ucar.edu' for 128.117.241.253
the secondary router interface would be named the 'b' router 'mlrb-n241.ucar.edu' for 128.117.241.254

DNS Contact

The information provided in the DNS contact field for the vlans and subnets pages is pulled directly from DNS per UCAR conventions. Specifically by querying the SOA record for the subnet using 'dig'.

For example:

dig soa -x 128.117.45.0

; <<>> DiG 9.2.4 <<>> soa -x 128.117.45.0
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 3579
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;0.45.117.128.in-addr.arpa. IN SOA

;; AUTHORITY SECTION:
117.128.in-addr.arpa. 0 IN SOA dns.ucar.edu. postmaster.ucar.edu. 200706121 28800 14400 604800 172800

;; Query time: 1 msec
;; SERVER: 128.117.64.11#53(128.117.64.11)
;; WHEN: Fri Jun 15 09:59:34 2007
;; MSG SIZE rcvd: 102

Address comments or questions about this Web page to the Network Engineering & Telecommunications Section at nets-www@ncar.ucar.edu. The NETS is part of the Computational & Information Systems Laboratory of the National Center for Atmospheric Research, which is sponsored by the National Science Foundation and managed by the University Corporation for Atmospheric Research. This website follows the UCAR General Privacy Policy and the NCAR/UCAR/UOP Terms of Use.