Does ospf auto summarize interarea networks11/20/2023 If the delay is not added before transmission over a link, the time in which the link-state advertisement (LSA) propagates over the link is not considered. What is the purpose of the variable IP-OSPF-Transmit-Delay?Ī.This variable adds a specified time to the age field of an update. You can use the command ip ospf retransmit-interval to set the retransmit interval. The link-state retransmit interval defines the time between retransmissions. LSAs are retransmitted until they are acknowledged. What is the link-state retransmit interval, and what is the command to set it?Ī.OSPF must send acknowledgment of each newly received link-state advertisement (LSA). If you want to enable authentication on some interfaces only, or if you want different authentication methods on different interfaces that belong to the same area, use the ip ospf authenticationinterface mode command. (In the command, xis the area number.)Ĭisco IOS Software Release 12.x also supports and enables authentication on a per-interface basis. Then, issue the area x authentication command to the OSPF router configuration to enable authentication. To configure simple password authentication for an area, use the command ip ospf authentication-key to assign a password of up to eight octets to each interface attached to the area. Authentication can be through simple passwords or through MD5 cryptographic checksums. Are OSPF routing protocol exchanges authenticated?Ī.Yes, OSPF can authenticate all packets exchanged between neighbors. For more information, refer to Troubleshooting Load Balancing Over Parallel Links with Cisco Express Forwarding. What algorithm is used by OSPF if equal cost routes exist?Ī.If equal cost routes exist, OSPF uses CEF load balancing. For more information, refer to OSPF Cost. Note: If ip ospf cost cost is used on the interface, it overrides this formulated cost. For example, in the case of Ethernet, it is 100 Mbps / 10 Mbps = 10. The formula to calculate the cost is reference bandwidth divided by interface bandwidth. How does OSPF calculate its metric or cost?Ī.OSPF uses a reference bandwidth of 100 Mbps for cost calculation. Therefore, the maximum value supported is 65,535. By default, reference bandwidth is 100 Mbps. How do I change the reference bandwidth in OSPF?Ī.You can change the reference bandwidth in Cisco IOS Software Release 11.2 and later with the ospf auto-cost reference-bandwidthcommand under router ospf. However, when the ip ospf network point-to-pointcommand is removed from R1 to 0 interface, the route 10.1.1.1 on R2 is seen as: 10.0.0.0/32 is subnetted, 1 subnets When checked in router R2 with the show ip route ospfcommand, the route 10.1.1.1 is seen as: R1 has the loopback configured with the ip ospf network point-to-pointcommand and advertises the loopback in OSPF. This is an expected behavior if ip ospf network point-to-multipointis configured.įor example, consider two routers (R1 and R2) connected via FastEthernet interface. ISDN dialer interface advertises /32 subnet instead of its configured subnet mask. In Cisco IOS® Software Releases 11.3T and 12.0, if the ip ospf network point-to-pointcommand is configured under loopbacks, OSPF advertises the loopback subnet as the actual subnet configured on loopbacks. For more information, refer to section 9.1 of RFC 2328. Why are loopbacks advertised as /32 host routes in OSPF?Ī.Loopbacks are considered host routes in OSPF, and they are advertised as /32. In the scope of this document, "OSPF" refers to OSPF version 2 and "IP" refers to IP version 4. OSPF version 3, introduced in Cisco IOS ®Software Releases 12.0(24)S, 12.2(18)S, and 12.2(15)T, is used to distribute IP version 6 routing information it is not explicitly covered in this document. The document describes the most frequently asked questions (FAQ) associated with the Open Shortest Path First (OSPF) protocol.
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