Hello Karthik,
route tagging is a useful tool to perform mutual redistribution between two routing protocols specially if multiple border routers are used for mutual redistribution between two routing domains.
The idea is to tag routes differently depending on their original routing domain to avoid re-injection of routing information on different redistribution points (nodes) to original routing domain.
The tag values to be used are design choices
The logic is the following:
when redistributing RIP routes into EIGRP skip all routes with route-tag = 88 because that value means RIP routes that actually have been imported from the same EIGRP domain ( on the other border node or simply some time ago)
of remaining RIP routes accept them but tag them with value 77.
The design objectives are achieved by using a second route-map that performs a dual action and it is used for importing EIGRP routes into RIP.
route-map red-eigrp-into-rip deny 10
match tag 77
route-map red-eigrp-into-rip permit 20
set tag 88
router rip
redistribute eigrp 100 route-map red-eigrp-into-rip
! seed metric
default-metric 5
!
router eigrp 100
! seed metric required for successful redistribution into EIGRP
default-metric 10000 100 1 255 1500
redistribute rip route-map rip_to_eigrp
!
the power of route tags is that they automatically adapt to changes: for example if a new prefix is added to EIGRP domain no changes in configuration are needed simply the new route will exist as not tagged route in EIGRP routing domain and as as a RIP route with tag 88 in the RIP routing domain.
Also the same configuration can be applied to both ASBR border routers.
Hope to help
Giuseppe