OSPF metric-type 1 vs metric-type 2

Redistributed as Metric-Type 2 (default redistribution method):

Rack7R4(config-router)#do sh run | s router ospf
router ospf 1
log-adjacency-changes
redistribute rip subnets
network 155.7.45.4 0.0.0.0 area 0
network 155.7.146.4 0.0.0.0 area 0

Rack7R6#sh ip route 204.12.7.0
Routing entry for 204.12.7.0/24
Known via “ospf 1”, distance 110, metric 20, type extern 2, forward metric 1
Last update from 155.7.146.4 on FastEthernet0/0.146, 00:05:09 ago
Routing Descriptor Blocks:
* 155.7.146.4, from 150.7.4.4, 00:05:09 ago, via FastEthernet0/0.146
Route metric is 20, traffic share count is 1

Redistributed as Metric-Type 1:

Rack7R4(config-router)#do sh run | s router ospf
router ospf 1
log-adjacency-changes
redistribute rip metric-type 1 subnets
network 155.7.45.4 0.0.0.0 area 0
network 155.7.146.4 0.0.0.0 area 0

Rack7R6#sh ip route 204.12.7.0
Routing entry for 204.12.7.0/24
Known via “ospf 1”, distance 110, metric 21, type extern 1
Last update from 155.7.146.4 on FastEthernet0/0.146, 00:00:03 ago
Routing Descriptor Blocks:
* 155.7.146.4, from 150.7.4.4, 00:00:03 ago, via FastEthernet0/0.146
Route metric is 21, traffic share count is 1

Output based from INE Volume I topology:

Screenshot 2014-01-05 01.59.06

Advertisements

OSPF Neighbor States

OSPF Neighbor States

Down

Attempt  / send hello

Init     / received hello (check hello/dead timers, netmasks, AREA ID, Auth)

Two Way  / hellos received by both neighbors – reset dead timer and wait for another hello. repeat (The only exception to this is the 2-way state, which is normal in a broadcast network. Routers achieve the full state with their DR and BDR only. Neighbors always see each other as 2-way)

Exstart  / Master(higher priority) and slave exchange DBD packets summary of LSDB

Exchange / DBDs ack and review LSR

Loading  / LSU exchange between Master/Slave

Full     / LSDB is the same

Now time to run the Dijkstra SPF algorithm and create routes for routing table

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0e.shtml

3 types of OSPF authentication

These are the three different types of authentication supported by OSPF.

Null Authentication—This is also called Type 0 and it means no authentication information is included in the packet header. It is the default.

Plain Text Authentication—This is also called Type 1 and it uses simple clear-text passwords.

MD5 Authentication—This is also called Type 2 and it uses MD5 cryptographic passwords.

Authentication does not need to be set. However, if it is set, all peer routers on the same segment must have the same password and authentication method. The examples in this document demonstrate configurations for both plain text and MD5 authentication.

CISCO LINK

MPLS VPN EIGRP vs OSPF

EIGRP uses the BGP cost community during redistribution on the PE router of the CE routes and the idea of POI (point of insertion) and automaticlly creates the ‘super backbone’ for EIGRP to use the Provider link over the backdoor links

OSPF use the SHAM link inside the VRF to create ‘super backbone’ area 0 over the Provdier network to change the link over the Provider to an IntraArea link instead of and InterArea link… And the shamlink sets the cost to a value lower than the backdoor link cost

ip unnumbered

using ip unnumbered has differences

use ip unnumbered on Point-to-Point

EIGRP – does a check for same subnet based on the interface being configured for ip address or ip unnumbered(thus point to point)
OSPF – sends the netmask as 0.0.0.0

switch ‘system mtu’ command OSPF between switch and router

The command “system mtu 1500” on switches is the default one. Even
when value is changed, it will not be stored in neither running-config
nor startup-config. On Catalyst 3550, this information is stored in a
separate file on the flash. On Catalyst 3560, you can’t see it, unless
you do “show system mtu”.

This is one of the well-know little gotchas on the actual lab exam.
You *have* to know how to solve this. Hence, when configuring routing
protocols on switches, make sure you know what their MTU is.

Part of the OSPF adjacency negotiation is MTU. This has to be the same on both ends of the link before the neighbor comes up

Then there are several ways to fix it. First is change the switch MTU (best practice) , second is change the MTU on the router’s interface (have seen this fail, not able to set manually by user) and third is use the ‘ip ospf mtu-ignore’ command on both interfaces.