FAQ
Q: What happens to the RIP learned routes whose network address is same as one of the directly connected IPs, when the prefix length is greater than, less than, or equal to, that of the directly connected interface?
All routes with greater prefix length and less prefix length will be displayed in the RIP routing table. The equal prefix- length entry will be discarded.
For example. if the 1.1.0.0/24, 1.1.0.0/25 and 1.1.0.0/23 routes are redistributed into RIP, and a neighbor has an interface with IP 1.1.0.2/24, the RIP route entry of the 1.1.0.0/24 network will not be available. But, the 1.1.0.0/23 and
1.1.0.0/25 entries will be available in the RIP routing table. The 1.1.0.0/24 entry is available as a directly connected entry in the routing table. If this interface is down, the RIP route will become active, until the interface comes up.
Q: When redistributing other routes to RIP, why does the redistributed route always override the routes learned by RIP?
RIP learned routes have lower priority than redistributed routes (for example, connected/static/ISIS). Therefore, the redistributed routes always override the routes learned by RIP.
Q: Why is the BGP session reset after any BGP capability is configured?
In BGP, capabilities are advertised in the OPEN message during session initialization. If a capability is enabled or disabled after the session is established, the BGP session needs to be reset, and a new capability is included in the OPEN message.
Q: How do I set up “neighbor send-community” in BGP?
The “neighbor send-community” is set up by default. By default, on receiving the communities attribute, the router re- announces them to the neighbor. This command does not appear in the list of available commands in the Router mode. It is visible only when the user has used the no neighbor send-community command. Please refer to the BGP Command Reference for details on how to use this command.
Use the show ip bgp neighbor command to confirm that the neighbor send-community is set up.
Q: What is Route Reflection used for?
Route Reflection is used in IBGP to resolve the IBGP full mesh problem. Configuring one or more routers as Route
Reflectors reduces the number of connections between BGP peers within an Autonomous System (AS).
The Route Reflecting BGP peer has to be configured with the peer addresses of all its route reflection clients. The Route Reflector is responsible for:
• Sending updates from a client peer to other client peers, as well as non-client peers.
• Sending updates from non-client peers to client peers.
Q: Can you explain more about the BGP “neighbor next-hop-self” command?
The neighbor next-hop-self command is only effective in the case of IBGP. For example:
EBGP IBGP
R3 ----------------------- R1 ----------------------- R2
On executing the neighbor <a.b.c.d> next-hop-self command on R1, the R1 router advertises the routes (if any) with the next-hop attribute that equals the R1 IP address.
This command is useful for advertising the routes learned by R1 from other routers, and are not reachable by R2.
Q: Does the “no bgp graceful restart” command turn off graceful restart? Or does it just set the parameters back to the default?
The no bgp graceful-restart command turns off the graceful restart functionality.
The no bgp graceful-restart restart-time and no bgp graceful-restart stalepath-time commands reset the timer values to the default values.
Q: Which BGP draft version is used to test conformance?
IP Infusion Inc. uses the IXIA ANVL test suite for testing conformance. The latest version of ANVL is based on draft- ietf-idr-bgp4-26.txt.
Q: Can I change the Area ID of an existing OSPF network configuration?
No, you cannot change the Area ID without deleting the existing configuration. You need to remove the network
A.B.C.D/X area Y before changing the area ID of this network.
For example, entering “network 10.73.0.0/16 area 0.0.0.5” when “network 10.73.0.0/16 area 0.0.0.1” already exists, will display a warning message.
Q: How do I display information about max-age? I used the “show ip ospf database max-age” command: max-age was not displayed.
The show ip ospf database max-age command maintains a list of the all the LSAs in the database that have reached the max-age (3600 seconds).
If the LSAs have not reached the max-age, it is not displayed. To test the functionality of max-age, follow these steps:
1. Connect two routers, R1 and R2 both of them running the OSPF daemon.
2. After a few minutes, kill the OSPF daemon on one of the routers (say on R2).
3. Wait for one hour to get a display of the list of LSAs that have reached the max-age on R1.
The following is a sample output of the show ip ospf database max-age command on R1:
# show ip ospf database max-age
OSPF Router process 100 with ID (3.3.3.4)
MaxAge Link States:
Link type: 7
Link State ID: 37.37.37.0
Advertising Router: 3.3.3.1
LSA lock count: 6
Link type: 7
Link State ID: 10.0.0.0
Advertising Router: 3.3.3.1
LSA lock count: 6
Link type: 7
Link State ID: 20.255.37.37
Advertising Router: 3.3.3.1
LSA lock count: 6
Q: How do I create a secondary loopback address? This address has to be advertised by LSAs to make it reachable from other routers and hosts.
Configure a secondary loopback address as follows:
(config)# interface lo
(config-if)# ip address A.B.C.D/32
For this loopback address to be advertised by LSAs, enable OSPF on this interface by configuring the routing process, and specifying the Process ID. The Process ID should be a unique positive integer identifying the routing process. Then define the interface and associate the area ID with the interface.
(config)# router ospf [process id]
(config-router)# network A.B.C.D/32 area 0