Posted by: Richard @ | February 7, 2008

Day 4 of Week 5

My apologies about the lack of updates over the last few days but I really haven’t moved forward too much this week, studying has been a bit start/stop all week.  I read the entire OSPF chapter of RSCG2 on Monday evening and that ended up being a complete waste of time!  I would say I had a hazy BSCI level of understanding of OSPF before reading the chapter (EIGRP being the primary IGP used by my employers) but after reading RSCG2’s interpretation of OSPF in high-level detail I just wanted to leave the IT industry altogether!  I believe this was down to the writing style of the RSCG2 author(s) not suiting me, it has caused me to approach reading the book as a chore and at the back of my mind I have known another option exists ….  I have now ordered volumes one and two of Jeff Doyle’s ‘Routing TCP/IP’ books and plan to use those as my primary learning resource for IGP’s, BGP, IPv6, and Multicast from now on.  The books cost me £80 which isn’t a huge sum of money and I believe the books will turn out to be priceless during my CCIE studies.  Jeff Doyle really does take technical writing to another level.

Tuesday night was a night off for both me and Leanne because it was Leanne’s birthday.  I took Leanne and the children to the local Italian restaurant, both of the girl’s had been to the doctors that afternoon for two injections each, they weren’t very happy about that and they didn’t feel too well afterwards…. this lead to the grandparents collecting two ‘unhappy’ children from the restaurant!  Despite this it was nice to get away from things for a couple of hours and spend some quality time with Leanne (and the very attentive waiter).  When I came back to studying I was feeling quite fresh – maybe I should build in some more breaks

Last night was a new beginning as far as OSPF studies are concerned; I have been a bit naughty and started to use an electronic copy of ‘Routing TCP/IP Volume 1’ whilst I wait for my hard copies, I justified this to myself because I have paid for the books and am now merely waiting for delivery, Jeff Doyle and his publisher have (or will) be rewarded for their time and efforts.  Following on from that I did manage to spend some time with OSPF last night and here is one of the tables that I copied down (and I have added a few notes):

OSPF Network Types

Type DR/ BDR Hello Interval (secs) ‘Neighbor’ required? >2 routers per subnet Configuration Notes
point-to-point No 10 No No ip ospf network point-to-point ·       e.g. T1/SONET
·       Always adjacent
·       Destination is always multicast IP address
·       Default type for frame-relay point-to-point sub-interfaces
Broadcast Yes 10 No Yes ip ospf network broadcast ·       e.g. Ethernet/FDDI/Token-ring
·       Destination can be multicast IP address or
·       Default for Ethernet
NBMA Yes 30 Yes Yes ip ospf network non-broadcast ·       e.g. Frame-relay/ATM
·       Destination is neighbour’s unicast IP address
·       PVC’s must exist – especially between DR & BDR
·       Default type for frame-relay physical and point-to-multipoint interfaces
point-to-multipoint No 30 No Yes ip ospf network point-to-multipoint(neighbor ‘ip-address’ cost ‘cost’) ·       e.g. Frame-relay/ATM
·       If neighbor is specified configure cost as well
point-to-multipoint NB No 30 Yes Yes ip ospf network point-to-multipoint non-broadcast(neighbor ‘ip-address’) ·       e.g. Classic IP over ATM
·       Collection of point-to-point networks
·       Destination is neighbour’s unicast IP address
Loopback No No ·       When point-to-point type is configured the configured network mask is advertised and not just a 32-bit host mask
·       Default type is point-to-multipoint (32-bit advert)
virtual link area ‘transit area no.’ virtual-link ‘dest. RID’ ·       ‘Unnumbered point-to-point’
·       Destination is neighbour’s unicast IP address

Cisco Type = AllSPFRouters (0100.5E00.0005) = AllDRouters (0100.5E00.0006)

What works together:
1) Broadcast to Broadcast
2) Non-Broadcast to Non-Broadcast
3) Point-to-Point to Point-to-Point
4) Point-to-Multipoint to Point-to-Multipoint
5) Broadcast to Non-Broadcast (match hello/dead timers)
6) Point-to-Point to Point-to-Multipoint (match hello/dead timers)

Tonight I found something I don’t recall covering during the BSCI course (I might be wrong) and that’s OSPF ‘age’ and how an originating router can prematurely set it to the ‘MaxAge’ value of 3600secs (1hr) to cause a re-flood and flush of a LSA out of all link-state databases (usually used when ‘MaxSequenceNumber’ is reached).  Here’s a link to some more ‘age’ information.

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