Posted by: Richard @ | February 11, 2008

Day 6 of Week 5 and the end of Week 5

Another seven days have passed and my CCIE studying hasn’t moved forward as far as I hoped it would L

Last week, I had reached a point that meant my study plan could have turned out to be a brilliant prediction of how my CCIE studies would progress – I’m usually not too great at judging how much time something will take so that was quite a shock to me.  Unfortunately, this week I have fallen about two days behind the study plan dates, this is mainly due to Monday night’s counter-productive reading, Tuesday night off, and only 1hrs worth of studying due to overtime during Friday evening.  Luckily, being a couple of days behind at this point in time shouldn’t turn out to cause me major problems because I have built in a two week ‘break’ which is due in another couple of weeks (after BGP).  Hopefully, I will be able to catch-up then J

I came across a feature I didn’t know existed during the last week:
ip ospf name-lookup
Ring any bells?  Well, it’s a mechanism that allows a Cisco router to perform reverse-DNS lookups to translate Neighbour ID’s/RID’s to meaningful names using its configured DNS servers (or local host entries), the names are used in all OSPF show EXEC commands, here’s an example:

R1#sho ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface       1   FULL/DR      00:00:37      FastEthernet0/0

R1(config)#ip ospf name-lookup
R1(config)#ip host R1_f0/0

R1#sho ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
R1_f0/0           1   FULL/DR         00:00:30      FastEthernet0/0

1) If a name server is configured (using ip name-server ‘ip-address’) and no local host entry exists (ip host…)  a reverse-dns lookup is sent to the configured DNS server
2) no name-server + no local host entry = broadcast reverse-DNS lookup (as long as ip domain-lookup is configured – required for any of this to work)

I have also put together a table to help me remember OSPF LSA types:


Desc. Sent by (types) What’s in it? Where’s it sent? Show Notes
1 Router LSA All All links, link states, outgoing cost of each link, and any known OSPF neighbors on the link Flooded within area show ip ospf database router Host route = stub network

Link State ID (within LSA) = Originating RID 

2 Network LSA DR on every multi-access network Represents a pseudonodeLists all attached routers (inc. DR) Flooded within area show ip ospf database network No metric field as cost = 0

Link State ID = DR’s interface to network

3 Network Summary LSA ABR’s Destinations outside area the ABR can reach Sent into an area that an ABR is attached to show ip ospf database summary Link State ID = IP address of network/subnet router is advertising

ABR also advertises the destinations within its attached areas into the backbone with Network Summary LSAs

Default routes external to the area, but internal to the OSPF autonomous system are this type

ABR originating includes the cost from itself to the destination the LSA is advertising – only a single LSA (even if multi routes are known)

Another router receives this LSA from an ABR à no SPF algorithm à add the cost of the route to the ABR and the cost included in the LSA à Because of dependency on an intermediate router this is distance vector behaviour à inter-area (why backbone area is required)

4 ASBR Summary LSA ASBR’s (& ABR’s) Same as Type 3 except destination = ASBR, not a network Sent into an area that an ABR/ASBR is attached to show ip ospf database asbr-summary Link State ID = RID of ASBR advertising

Destination is a host address, and the mask is zero; the destination advertised by an ASBR Summary LSA will always be a host address because it is a route to a router

5 AS External LSA ASBR A destination/default route external to the OSPF AS Flooded throughout AS except stub areas show ip ospf database external AKA ‘Autonomous System External LSAs’

Link State ID = IP address of destination

Only LSA types in the database that are not associated with a particular area

6 Group Membership LSA Multicast routers     show ip ospf database nssa-external NOT SUPPORTED BY CISCO

MOSPF routes packets from a single source to multiple destinations, or group members, which share a class D multicast address

7 NSSA External LSA ASBR within NSSA’s Almost identical to an AS External LSA Flooded only within the not-so-stubby area in which it was originated show ip ospf database nssa-external Converted from type 7 into type 5 before flooding into the backbone (as long as p-bit is set to 1)
8 External Attributes LSA         NOT SUPPORTED BY CISCO

Idea was to remove the need to run iBGP

9 Opaque LSA (link-local scope)   Standard LSA header followed by application-specific information      
10 Opaque LSA (area-local scope)
11 Opaque LSA (AS scope)

One last thing that was brought to my attention over the last seven days is a very useful command that I’m surprised I missed when working on an article covering macro’s for, the command is show parser dump ‘command type’:

R1#sho parser dump exec
 Mode Name :exec
15 upgrade
15 upgrade rom-monitor preference readonly
15 upgrade rom-monitor preference upgrade
15 upgrade rom-monitor file <URL>
15 upgrade filesystem monlib
1 clear
1 clear counters Line <tty>
1 clear counters
1 clear host vrf <string> <string>
1 clear host view <string> all
1 clear host view <string>
1 clear host view default
1 clear host
1 clear parser cache
1 clear tgrep counters csr dial-peer <1-2147483647>
1 clear tgrep counters csr dial-peer *
1 clear tgrep counters csr carrier
1 clear tgrep counters csr trunk-group
1 clear tgrep counters csr *
1 clear tgrep counters ac
1 clear tgrep counters
1 clear tgrep neighbor <address>
1 clear tgrep neighbor *
1 clear redundancy counters
1 clear redundancy history
1 clear logging xml
1 clear logging
1 clear access-list counters <1-199>
1 clear access-list counters <1300-2699>
1 clear access-list counters <string>
1 clear access-list counters
…….. etc etc ……..

The command above displays all the available commands available for a given command type (in this example ‘exec)’ – very useful when you know the first word of a command but nothing else…..

The command that was very close to the one above is show parser macro – it displays all macro’s available to be referenced by the macro apply command including the hidden Cisco default templates.

Here is the breakdown of my fifth week of studying:

Study time:
Study Hours = 9.5  inc.
Lab Hours = 0

Total study time so far:
Total Study Hours = 67  inc.
Total Lab Hours = 9.5

What I have studied this week:

Recent test scores:
Nothing this week

I plan to spend two more days on OSPF and route summarisation and then move onto to BGP on Wednesday.

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