872 BigIron RX Series Configuration Guide53-1001986-01Configuring IPv4 address family route parameters28For example, if the router has a path from RIP, from OSPF, and IPv4 IS-IS to the same destination,and all the paths are using their protocols’ default administrative distances, the router selects theOSPF path, because that path has a lower administrative distance than the RIP and IPv4 IS-ISpaths.Here are the default IPv4 administrative distances on the device:• Directly connected – 0 (this value is not configurable)• Static – 1 (applies to all static routes, including default routes)• EBGP – 20• OSPF – 110• IPv4 IS-IS – 115• RIP – 120• IBGP – 200• Local BGP – 200• Unknown – 255 (the device will not use this route)Lower administrative distances are preferred over higher distances. For example, if the devicereceives routes for the same network from IPv4 IS-IS and from RIP, it will prefer the IPv4 IS-IS routeby default.To change the administrative distance for IPv4 IS-IS routes, enter the following command at theIPv4 IS-IS unicast address family configuration level.BigIron RX(config-isis-router-ipv4u)# distance 100Syntax: [no] distance This command changes the administrative distance for all IPv4 IS-IS routes to 100.The parameter specifies the administrative distance. You can specify a value from 1 –255. (Routes with a distance value of 255 are not installed in the routing table.) The default forIPv4 IS-IS is 115.Configuring summary addressesYou can configure summary addresses to aggregate IS-IS route information. Summary addressescan enhance performance by reducing the size of the Link State database, reducing the amount ofdata the device needs to send to its neighbors, and reducing the CPU cycles used for IS-IS.When you configure a summary address, the address applies only to Level-2 routes by default. Youcan specify Level-1 only, Level-2 only, or Level-1 and Level-2 when you configure the address.To configure a summary address, enter a command such as the following.BigIron RX(config-isis-router-ipv4u)# summary-address 192.168.0.0 255.255.0.0This command configures a summary address for all Level-2 IS-IS route destinations between192.168.1.0 – 192.168.255.255.Syntax: [no] summary-address [level-1 | level-1-2 | level-2]The parameters specify the aggregate address. The mask indicates thesignificant bits in the address. Ones are significant, and zeros allow any value. In the commandexample above, the mask 255.255.0.0 matches on all addresses that begin with 192.168 andcontain any values for the final two octets.
