Network Bulls
www.networkbulls.com
Best Institute for CCNA CCNP CCSP CCIP CCIE Training in India
M-44, Old Dlf, Sector-14 Gurgaon, Haryana, India
Call: +91-9654672192
IPv6 routing protocols can perform route redistribution, much like IPv4 route redistribution
(as detailed in Chapter 9, “Basic IGP Redistribution,” and Chapter 10, “Advanced IGP
Redistribution”). This section shows a few examples to confirm those similarities and
compares IPv4 and IPv6 route redistribution.
The following list summarizes some of those key similarities between both IPv4 and IPv6
route redistribution:
■ Redistribution takes routes from the IP routing table, not from the topology tables
and databases controlled by the source routing protocol.
■ Route maps can be applied when redistributing for the purpose of filtering routes,
setting metrics, and setting route tags.
■ IPv6 routing protocols use the same default administrative distances, with the same
basic mechanisms to override those defaults.
■ The same basic mechanisms exist in IPv6 to defeat routing loop problems: administrative
distance, route tags, and filtering.
■ The routing protocols use the same default administrative distance (AD) settings for
internal and external routes.
■ The redistribution configuration uses practically the same syntax with the same
commands.
Some differences do exist, both in configuration and in concept, as follows:
■ Any matching done with distribution lists or route maps would use IPv6 prefix lists
and IPv6 ACLs, which match based on IPv6 prefix and length.
■ The IPv6 version of the redistribute command takes only routes learned from an IGP
but by default does not take connected routes on interfaces enabled for that IGP. To
also redistribute those connected routes, the redistribute command must include the
include-connected parameter. When an IPv4 routing protocol redistributes from an
IGP, it always attempts to take both the IGP-learned routes and the connected routes
for interfaces enabled for that IGP.
■ Unlike OSPFv2, OSPFv3 does not require a subnets parameter on the redistribute
command, because IPv6 does not maintain the IPv4 concept of classful networks and
the subnets inside those classful networks.
Key
Topic
www.CareerCert.info
596 CCNP ROUTE 642-902 Official Certification Guide
R1 R3
R2
2000:0:0:0::/64
2000:0:0:1::/64
2000:0:0:2::/64 2000:0:0:3::/64
2000:0:0:4::/64
RIP left OSPF
S0/0/1 F0/1
F0/0
Figure 17-3 Redistribution Plan
■ IPv6 redistribution ignores the “local” routes in the IPv6 routing table (the /128 host
routes for a router’s own interface IPv6 addresses). IPv4 has no equivalent concept.
Redistributing without Route Maps
As with IPv4 redistribution, IPv6 redistribution can be done without applying a route
map. The first redistribution example shows such a case, with router R2 performing the redistribution.
In this case, R2 redistributes routes learned from an OSPF domain on the
right, into a RIP domain on the left, without applying a route map. Figure 17-3 shows the
two routing domains and the IPv6 subnets used.
Example 17-8 shows the redistribution configuration on Router R2, which takes routes
from OSPF process number 5 and redistributes them into RIP process “left.” The example
begins with a show ipv6 route command on R2 to list the routes that could be redistributed,
and ends with those routes being seen on Router R1.
Example 17-8 Redistributing from OSPF into RIP, with Default Metrics
R2# show ipv6 ospf interface brief
Interface PID Area Intf ID Cost State Nbrs F/C
Fa0/1 5 0 4 1 BDR 1/1
R2# show ipv6 route
IPv6 Routing Table - Default - 9 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, M - MIPv6, R - RIP, I1 - ISIS L1
I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary, D - EIGRP
EX - EIGRP external
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
R 2000::/64 [120/2]
via FE80::213:19FF:FE7B:5026, Serial0/0/1
C 2000:0:0:1::/64 [0/0]
www.CareerCert.info
Chapter 17: IPv6 Routing Protocols and Redistribution 597
via Serial0/0/1, directly connected
L 2000::1:213:19FF:FE7B:5004/128 [0/0]
via Serial0/0/1, receive
C 2000:0:0:2::/64 [0/0]
via FastEthernet0/1, directly connected
L 2000:0:0:2::2/128 [0/0]
via FastEthernet0/1, receive
O 2000:0:0:3::/64 [110/2]
via FE80::213:19FF:FE7B:6588, FastEthernet0/1
C 2000:0:0:4::/64 [0/0]
via FastEthernet0/0, directly connected
L 2000::4:213:19FF:FE7B:5004/128 [0/0]
via FastEthernet0/0, receive
L FF00::/8 [0/0]
via Null0, receive
R2# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)# ipv6 router rip left
R2(config-rtr)# redistribute ospf 5 include-connected
R2(config-rtr)# ^Z
R2#
! The next command is executed on router R1
R1# show ipv6 route rip
IPv6 Routing Table - Default - 8 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, M - MIPv6, R - RIP, I1 - ISIS L1
I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary, D - EIGRP
EX - EIGRP external
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
R 2000:0:0:2::/64 [120/2]
via FE80::213:19FF:FE7B:5004, Serial0/0/0
R 2000:0:0:3::/64 [120/3]
via FE80::213:19FF:FE7B:5004, Serial0/0/0
R 2000:0:0:4::/64 [120/2]
via FE80::213:19FF:FE7B:5004, Serial0/0/0
The brief configuration shows both the simplicity and one difference in the IPv4 and IPv6
redistribution configuration. First, the redistribution function works with only the
redistribute ospf 5 command, which takes routes from R2’s OSPF 5 process. However,
the redistribute command has the include-connected keyword, which tells RIP to not
only take the OSPF-learned routes for 2000:0:0:3::/64, but also the connected route for
2000:0:0:2::/64, the connected route off R2’s F0/1 interface. The beginning of the example
lists a show ipv6 ospf interface brief command, which lists that only F0/1 has been enabled
for OSPF.
www.CareerCert.info
598 CCNP ROUTE 642-902 Official Certification Guide
The show ipv6 route rip command on R1, at the end of the example, shows that R2 indeed
redistributed the two routes from the OSPF side of Figure 17-3.
Redistribution into RIPng uses a metric as taken from the IPv6 routing table by default. In
this case, the output from R1 at the end of the example lists the two redistributed routes
with metrics 2 and 3. You can see from the earlier output in the example that R2’s metric
for its OSPF route to 2000:0:0:3::/64 was 2, so R3’s metric is now listed as 3.
Using RIPng’s default action to take the integer metric from the source IGP worked in this
case, but in most cases, the metric should be set via configuration. OSPF metrics will often
be more than the maximum usable RIP metric of 15, making these routes instantly unusable
in RIP. Redistributing from EIGRP into RIP would not work either, given the
relatively large integer metrics calculated by EIGRP. So when redistributing into RIP,
change the configuration to set the metric. For instance, using the command redistribute
ospf 5 include-connected metric 3 would have set the default metric for all redistributed
routes and avoided such problems.
Redistributing with Route Maps
IPv6 redistribution can also call route maps, for all the usual reasons: setting metrics for
different routes, filtering routes, and setting route tags, to name a few. To demonstrate the
configuration, Example 17-9 shows another example, using the same design in Figure 17-
3. In this case, Router R2 redistributes RIP routes into OSPF, with the following criteria:
■ Redistribute only LAN subnets, with OSPF metric 200.
■ Filter all other subnets.
Example 17-9 shows the configuration on R2 and the resulting OSPF routes on R3.
Example 17-9 Redistributing from RIP into OSPF, Using a Route Map
R2# show run
! unrelated lines omitted
ipv6 router ospf 5
router-id 2.2.2.2
redistribute rip left route-map only-RIP-lan include-connected
!
ipv6 router rip left
redistribute ospf 5 metric 3 include-connected
!
ipv6 prefix-list rip-to-ospf seq 5 permit 2000::/64
ipv6 prefix-list rip-to-ospf seq 10 permit 2000:0:0:4::/64
!
route-map only-RIP-lan permit 10
match ipv6 address prefix-list rip-to-ospf
set metric 200
R3# show ipv6 route ospf
IPv6 Routing Table - Default - 7 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
www.CareerCert.info
Chapter 17: IPv6 Routing Protocols and Redistribution 599
B - BGP, M - MIPv6, R - RIP, I1 - ISIS L1
I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary, D - EIGRP
EX - EIGRP external
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
OE2 2000::/64 [110/200]
via FE80::213:19FF:FE7B:5005, FastEthernet0/0
OE2 2000:0:0:4::/64 [110/200]
via FE80::213:19FF:FE7B:5005, FastEthernet0/0
First, the configuration shows an IPv6 prefix list and a route map that uses a match ipv6
command that refers to the prefix list. The prefix list works just like an IPv4 prefix list,
other than matching with the IPv6 prefix format rather than IPv4. The route map works
with the same logic as well, in this case referencing the IPv6 prefix list with the match
ipv6 address prefix rip-to-ospf command. The route map matches the two LAN subnets
in the RIP domain with the first route map clause and sets the metric to 200. The implied
deny clause at the end of the route map matches all other routes, which makes R2 filter all
other routes from being redistributed into OSPF. As a result, the serial IPv6 subnet,
2000:0:0:1::/64, is filtered by the redistribution process.
The show ipv6 route ospf command on R3 at the end of the example confirms that R3
learned routes for both LAN subnets in the RIP domain but no other routes. Of particular
interest, note that OSPFv3 lists the route as OSPF external Type 2, because just like
OSPFv2, OSPFv3 defaults to redistribute routes as external Type 2 routes. Note also that
the output lists metrics for each route as 200, because R2 set the metric to 200, and OSPF
does not add anything to the metric of E2 routes.
No comments:
Post a Comment