From: John Matus (John.Matus@tokiom.com)
Date: Mon Nov 14 2005 - 18:37:46 GMT-3
i'm curious about "best-practices" with tags for dealing w/ multiple points
of redistribution.
here's the diagrams
|-----a----eigrp----R1--b-----ospf----------R2---c----rip-----|
the method that i always use for redistributions, let's say for R1 would
be:
router eigrp 100
redis ospf 1 metric 1 1 1 1 1 route-map o2e
router os 1
redis eigrp sub route-map e2o
route-map o2e deny 10
match tag 90
route-map o2e permit 20
set tag 110
route-map e2o deny 10
match tag 110
route-map e2o permit 20
set tag 90
....where i use the AD of the protocol for the tag value. BUT
if i do the same for R2 the tags would look like this
| -----------(90)----R1----(110)----R2-----(120)-----------|
so, the locally originating eigrp routes enter R1 w/out a tag and get
assigned a tag 90 as they enter ospf on subnet b, preventing them from
returning back thru R1 to subnet a b/c they are blocked by the by the:
route-map o2e deny 10
match tag 90
but as the prefixes traverse through R2 to subnet c they then get assigned
the tag value of 110 and get blocked from returning to subnet b by a
similar route-map there.
route-map r2o deny 10
match tag 110
route os 1
redis rip sub route-map r2o
route rip
redis ospf 1 metric 1 route-map o2r
route-map r2o deny 10
match tag 110
route-map r2o permit 10
set tag 120
route-map o2r deny 10
match tag 120
route-map o2r permit 20
set tag 110
ok, to further complicate this let's creat a loop
R3>--a--eigrp--R1--b--ospf--R2--c---rip--R3--a--eigrp
1.1.1.1
R3 is connected to R1 and R2 in a loop. prefix 1.1.1.1 is on subnet a
router rip
redis eigrp 100 metric 1 route-map e2r
router eigrp 100
redis rip metric 1 1 1 1 1 route-map r2e
route-map e2r deny 10
match tag 120
route-map e2r permit 20
set tag 90
route-map r2e deny 10
match tag 90
route-map r2e permit 20
set tag 120
so, as route 1.1.1.1 enters R1 is picks up the tag 90, and is blocked from
returning to subnet a, but allowed to go from subnet b to subnet c where it
is reassigned the tag 110, thus preventing it from returning to subnet b,
but allowing to to go to subnet a where it picks up the tag 120..........OK
SHIT, this is were R1 see's the route 1.1.1.1 as being directly connected
as well as being learned from R3 with a metric AD of <i think> 170 <?>.
sooooooo. at this point R1 would just not install the route from R3 in it's
table b/c the connected route has a lower AD, thus no routing loop<?>...and
i'm hoping that at the same time R3 will install 1.1.1.1 as a connected
route as well because it's AD is lower than the route learned from R1 to R2
to R3, thus no sub-optimal routing as well.
yeah? just thinking out loud. any comments?
Regards,
John D. Matus
Technical Support / PAS
Fujitsu Consulting
626-568-7716
John.Matus@tokiom.com
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