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From: Alex Zinin (azininNEXSI.COM)
Date: Wed May 16 2001 - 13:22:47 CDT
In this particular case you don't need the BB routers to know
which path exactly (RT1-RT2-RT4-N1 or RT1-RT3-RT5-N1) is the
best, since they will forward traffic to RT1 and RT1 will make
the decision based on it's own routing table.
In a situation where there are two ABRs, only one has a VL,
but the best path goes through the other, the second ABR would
have to be configured with a VL for the BB routers to see
-- Alex Zinin
Tuesday, May 15, 2001, 8:03:56 PM, Li Zhong Jie wrote:
> Alex, > Sorry I have forgetton to refer to the figures discussed. > figure6 refers to RFC2328:Figure 6 > N1 where you cann't understand refers to N1 in RFC2328:Figure 17. > Would you explain my question then?
> Li >> Li, >> >> See inline, pls. >> >> >> > 4. Route calculation. >> >> > 4.1 Routers in all areas have seen new type-3 and type-4 LSAs, >> > so they redo inter-area and ASE route calculation >> >> > 4.2 When ABRs calculate inter-area routes above, they consider only >> > BB summaries. If any new route has been installed, this >> > triggers another round of summary-LSA origination (see 5) >> >>here should add? >> >> 4.3 when an ABR connects to a transit area,it should consider also >> >> transit area summaries. If any new route has been installed,this >> >> triggers another round of summary-LSA origination (see 5) >> >> yes, we may have to announce updated backbone routes to non-backbone >> areas. >> >> >> my question occurs here: >> >> >> in 4.3, if the router's inter area routes are updated,should the resulting >> >> routing table entry be advertised to BB area? >> >> No. 16.3 leaves updated routes associated with the BB and we don't >> announce routes back to the areas they belong to. >> >> >> If not,other routers in BB area >> >> would not gain from the shortcut via transit area. e.g.in Figure 6,RT7 finds >> >> its way to N9-N11 via RT7->N6->RT10-->N9-N11 with total cost 15,how RT5 knows >> >> this shortcut to N9-N11 and selects RT7 instead of RT6 as next hop? >> >> You'd need to have a VL to RT7. >> >> >> >> if the router's intra area routes are updated(suppose Network N1),how the resulting >> >> routing table entry is known to BB area's other routers so that they can update >> >> their route table entry describing N1? >> >> Couldn't decipher this... What is the ABR and where are the VLs here? >> >> Alex. >> >> >>