Intra-area, inter area, El, E2, Nl, and N2.
A default route is used if there is not a specific entry in the routing table for the destination.
WEIGHT, LOACL_PREF, AS_PATH, MED
Routing moves a letter or telephone call to the access layer.
Switching makes the final delivery. A switching decision is made on the part of the address that is not used in routing.
An OSPF interface metric is determined from the interface bandwidth. By default, all IS¬-IS interface metrics are equal to @Therefore, the EIGRP route is preferred.
Hold-down timers prevent regular update messages from reinstating a route that might have gone bad. Hold-down timers also tell routers to hold for a period of time any changes that might affect routes.
OSPF databases on routers in the same area must be identical. If route summarization was allowed within an area, some routers would have specific routes and some routers would have summary routes for routers in the area. If this were allowed, the databases for the area would never agree.
To connect a nonzero area to the backbone if the nonzero area becomes disconnected from the backbone. A virtual link can also be used if the backbone, or area 0, becomes discontiguous.
Redistribution of Level 2 routes into an area as Level l routes.
64 because 2 bits are needed for the hosts on the network, leaving 6 bits for the subnet.
Here are the four timers that IP RIP uses to regulate its performance:
This is normal. On point-to-point and point-to-multipoint networks, there are no designated routers (DRs) or backup designated routers (BDRs).
OSPF intra-area and inter area routes, and possibly a default route. External routes from ABRs are blocked, and external routes from ASBRs are converted to Nl or N2 routes.
Multicast forwarding decisions are based on the entries in the unicast IP routing table. Multicast is not dependent on how the unicast IP routing table was built; you c use any dynamic interior routing protocol, static routes, or a combination of the two.
Two or more RPs are configured with the same IP address. The IP addresses of the RPs are advertised using a unicast IP routing protocol. Each multicast router chooses the closet RP. If an RP fails, the routers switch to the next nearest RP after the unicast ip routing protocol converges. The MSDP is used between RPs to exchange active multicast source information.
WEIGHT has only local significance and is not advertised to BGP peers.
A broadcast domain defines a group of devices that receive each others’ broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower your network will be. This is because every device that receives a broadcast must process it to see if the broadcast is intended for it.
The way you enable IGRP on a Cisco router is similar to the way you enable RIP, except you specify IGRP as the protocol and add an autonomous system number.
For example: RouterA(config)#router igrp 10 (10 is the AS number)
The LOCAL _PREF attribute is advertised throughout the autonomous system.
The show ip route command displays the Cisco routing table’s contents.
Also known as the gateway of last resort, a default route is a special type of static route with an all-zeros network and network mask. The default route is used to route any packets to a network that a router does not directly know about to a next-hop router. By default, if a router receives a packet to a destination network that is not in its routing table, it drops the packet. When a default route is specified, the router does not drop the packet. Instead, it forwards the packet to the IP address specified in the default route.
BGP checks the NEXT HOP attribute to determine if the NEXT HOP is accessible or in the IP routing table.
OSPF intra-area routes and a default route. OSPF inter area and external routes are not advertised into a totally stubby area.
When a summary address is created with an IGP (EIGRP, OSPF, and IS-IS), the specific routes of the summary are not advertised. BGP advertises the summary, and all the specific routes of the summary unless they are specifically suppressed.
A Routing protocol defines the set of rules used by a router when it communicates with neighboring routers. Routing protocols listens for packets from other participants in order to learn and maintain a routing table.
When a router notices that a directly connected subnet has changed state, it immediately sends another routing update out its other interfaces rather than waiting for the routing update timer to expire. Triggered updates are also known as Flash updates.
A RP is the focal point for multicast traffic. Traffic is forward to the RP from multicast sources. The RP then forwards traffic to multicast receivers.
If a router has more than one route to the same IP prefix, the best path is the one with the highest WEIGHT value.
OSPF intra-area routes and a default route. External routes from ABRs are blocked, and external routes from ASBRs are converted to Nl or N2 routes.
Switches and bridges are used to break up collision domains. They create more collision domains and fewer collisions. Routers are used to break up broadcast domains. They create more broadcast domains and smaller broadcast areas.
Used with PIMSM Auto-RP and version @if the RPs fail, the router reverts to dense mode.
Convergence is when all routers have consistent knowledge and correct routing tables.
An Area Border Router (ABR).
By default, all routes are advertised into all OSPF areas. This includes inter area OSPF routes and external routes that have been injected into OSPF. By default, IS-IS does not advertise inter area or external routes into an area, but injects a default route.
Sometimes you do not want RIP updates to propagate across the WAN, wasting valuable bandwidth or giving out valuable information about your internetwork. The easiest way to stop RIP updates from propagating out an interface is to use the passive-interface global configuration command.
The rule of split horizon is that it is never useful to send information about a route back in the direction from which the original update came.
The three types of routes are static routes, dynamic routes, and default routes.
Static routes are routes that an administrator manually enters into a router. Dynamic routes are routes that a router learns automatically through a routing protocol.
The router with the highest interface priority will be the router ID. If all the interface priorities on the multi-access network are the same, the router with the highest router ID will be the DR.
An NSAP address has a length of8 to 20 bytes and consists of three components:
One to 13 byte area id
Six byte system id
One byte NSAP selector that is always equal to zero for a router