OSPF Series 9: Route Filtering and Route-Maps

Prefix-Lists

Prefix-lists are used to match routes as opposed to traffic. Two things are matched:

• The prefix (the network itself)

• The prefix-length

OSPF Series 8: Prefix Lists

Prefix Lists

Example 1)

access-list 1 permit 1.2.3.0 0.0.0.255

ip prefix-list LIST permit 0.0.0.0/0 le 32

This means:

Check the first 0 bits of the prefix 0.0.0.0 The subnet mask must be less than or equal to 32

OSPF Series 7: Example of OSPF Path Preferences, Troubleshooting neighborship stuck in various OSPF States

SCENARIO: Path Preferences:

• Configure Router-IDs on each router

• COnfigure IP address of interfaces in each router and add them using network command of OSPF

• Note: there is no need to configure static routes on MT708 as both the links are directly connected. MT708 doesn’t run OSPF.

• (On MT704,

OSPF Series 6: OSPF Areas, OSPF Redistribution, Type-3 LSA, Type-5 LSA, Prefix Lists, Administrative Distance and Metric in OSPF

OSPF AREAS:

• It is specific to interface (given in the network command)

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To make a router in OSPF as Autonomous System Border Router (ASBR) that connects it to another AS running static routing, then, use

• #router ospf 1
• #redistribute static //if the other external AS is using static routing

(OR)

#redistribute connected

OSPF Series 5: Link State Updates, Advertisements and Message Formats

LS Updates (and Advertisements):

• Note there is no LS Advertisement packet as such. Link State Update is the type of OSPF packet that carries many LS advertisements

• Each Link State Update packet carries a collection of link state advertisements one hop further from its origin. Several link-state advertisement may be included in a single LS Update packet. If any router notices a change in its networks, it sends that particular type of LS Update to the DR and BDR.

• Link State Update (carries Advertisements), it’s format is as given below: