Generally speaking, you have very little direct control of the FA selection.
In an NSSA area, it will be one of the ASBRs addresses advertised in OSPF (with preference given to Loopbacks over all other interfaces). In a non-NSSA area, when conditions are satisfied for the FA to exist (next-hop is known by OSPF, exit interface is broadcast or non-broadcast and is not passive), the FA will be set to the next-hop of the external route being redistributed into OSPF. So, you can manipulate some of those values - create new Loopback interfaces for the NSSA and change the next-hop for non-NSSA areas, but other than that, you can't manually configure what the FA will be. -- Marko Milivojevic - CCIE #18427 (SP R&S) Senior CCIE Instructor / Managing Partner - IPexpert :: Free Video Training: http://youtube.com/IPexpertInc :: Social: http://twitter.com/@icemarkom | http://fb.me/ccie18427 :: IPexpert: http://www.ipexpert.com/Communities | +1-810-326-1444 On Mon, Dec 2, 2013 at 7:52 PM, Hamed Shittu <[email protected]> wrote: > All, > > Need some clarification, I made one of Marko's ospf articles into a bigger > ospf domain, and this question came up--not sure if there is an answer > already ... > > Question: who selects ip address to use as Forward (FW) address the ASBR ? > can this be influence manually... > > here is the link to the article : > http://blog.ipexpert.com/2010/09/27/quick-look-into-ospf-database-nssa-external-lsa/ > > before i added a router(r6) to R1 ( using Serial interface) this how the > external db looks like on R4: > > R4#sh ip os database nssa-external > > OSPF Router with ID (4.4.4.4) (Process ID 1) > > Type-7 AS External Link States (Area 145) > > LS age: 905 > Options: (No TOS-capability, Type 7/5 translation, DC) > LS Type: AS External Link > Link State ID: 11.11.11.11 (External Network Number ) > Advertising Router: 1.1.1.1 > LS Seq Number: 80000002 > Checksum: 0xBDF1 > Length: 36 > Network Mask: /32 > Metric Type: 2 (Larger than any link state path) > TOS: 0 > Metric: 20 > Forward Address: 145.145.145.1 > External Route Tag: 0 > > > > After adding R6 to R1.... here is the DB on R4: > > R4#sh ip os database nssa-external > > OSPF Router with ID (4.4.4.4) (Process ID 1) > > Type-7 AS External Link States (Area 145) > > LS age: 3 > Options: (No TOS-capability, Type 7/5 translation, DC) > LS Type: AS External Link > Link State ID: 11.11.11.11 (External Network Number ) > Advertising Router: 1.1.1.1 > LS Seq Number: 80000003 > Checksum: 0x85AD > Length: 36 > Network Mask: /32 > Metric Type: 2 (Larger than any link state path) > TOS: 0 > Metric: 20 > Forward Address: 16.16.16.1 > External Route Tag: 0 > > > the FW add changed on R4 when i brought a link ( serial on R1 connecting > to R6) > > configs: > > R4#sh run | s router > router ospf 1 > router-id 4.4.4.4 > log-adjacency-changes > area 145 nssa > network 4.4.4.4 0.0.0.0 area 0 > network 24.24.24.4 0.0.0.0 area 0 > network 45.45.45.4 0.0.0.0 area 0 > network 145.145.145.4 0.0.0.0 area 145 > > > R1#sh run | s router > router ospf 1 > router-id 1.1.1.1 > log-adjacency-changes > area 145 nssa > redistribute connected subnets route-map CON-to-OSPF > network 16.16.16.1 0.0.0.0 area 145 > network 145.145.145.1 0.0.0.0 area 145 > > > > > ------------------------------------------------------------------------------ > This electronic mail (including any attachments) may contain information > that is privileged, confidential, and/or otherwise protected from > disclosure to anyone other than its intended recipient(s). Any > dissemination or use of this electronic email or its contents (including > any attachments) by persons other than the intended recipient(s) is > strictly prohibited. If you have received this message in error, please > notify us immediately by reply email so that we may correct our internal > records. Please then delete the original message (including any > attachments) in its entirety. Thank you. > _______________________________________________ > Free CCIE R&S, Collaboration, Data Center, Wireless & Security Videos :: > > iPexpert on YouTube: www.youtube.com/ipexpertinc > _______________________________________________ Free CCIE R&S, Collaboration, Data Center, Wireless & Security Videos :: iPexpert on YouTube: www.youtube.com/ipexpertinc
