Introduction:
As we know OSPF is link state routing protocol that works on the concept of areas. All routers in area must have same LSDB (link state database); hence OSPF summarization can do only on the border routers. There are two types of summarization you can do in OSPFv3:
•Inter-area route summarization
•External route summarization:
You configure inter-area route summarization on ABRs, summarizing routes between areas in the autonomous system. To take advantage of summarization, assign network numbers in areas in a contiguous way to be able to lump these addresses into one range.
External route summarization is specific to external routes that are injected into OSPFv3 using route redistribution. You should make sure that external ranges that are being summarized are contiguous. Summarizing overlapping ranges from two different routers could cause packets to be sent to the wrong destination. Configure external route summarization on ASBRs that are redistributing routes into OSPF.
In this document we will discussed on OSPFv3 inter-area route summarization. Summarization concepts are same for OSPV3 as for OSPFv2, even commands remain the same.
Please also go through IPv4 OSPF inter-area summarization document to get more knowledge.
Background:
In following example router ABR is directly connected to R1 in area 1 and to R2 in backbone area0.On R1 there are three Vlans interfaces configured with the following IPv6 addresses:
VLAN 1: FC00:1:1:2001::1/64
VLAN 2: FC00:1:1:2011::1/64
VLAN 3: FC00:1:1:2021::1/64
Topology Diagram:
Initial configuration:
R1
ABR
R2
ipv6 unicast-routing ! interface Loopback0 ip address 1.1.1.1 255.255.255.255 ! interface FastEthernet0/0 no ip address speed 100 full-duplex ipv6 address 2001::1/64 ipv6 ospf 100 area 1 ! interface FastEthernet1/0 ! interface FastEthernet1/1 switchport access vlan 2 ! interface FastEthernet1/2 switchport access vlan 3 ! interface Vlan1 no ip address ipv6 address FC00:1:1:2001::1/64 ! interface Vlan2 no ip address ipv6 address FC00:1:1:2011::1/64 ! interface Vlan3 no ip address ipv6 address FC00:1:1:2021::1/64 ! ipv6 router ospf 100 log-adjacency-changes | ipv6 unicast-routing ipv6 cef ! interface Loopback0 ip address 10.10.10.10 255.255.255.255 ! interface FastEthernet1/0 no ip address duplex full speed 100 ipv6 address 2001::1/64 ipv6 ospf 100 area 1 ! interface FastEthernet1/1 no ip address duplex full speed 100 ipv6 address 2002::1/64 ipv6 ospf 100 area 0 ! ipv6 router ospf 100 log-adjacency-changes !
| ipv6 unicast-routing ! interface Loopback0 ip address 2.2.2.2 255.255.255.255 ! interface FastEthernet0/0 no ip address speed 100 full-duplex ipv6 address 2002::2/64 ipv6 ospf 100 area 0 ! ipv6 router ospf 100 log-adjacency-changes !
|
R2 in area 0 learns Type3 LSA for above mention VLANs via ABR and installed them into routing table as shown in below output:
R2#sh ipv6 route ospf | sec O
O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
OI 2001::/64 [110/11]
via FE80::C803:72FF:FE88:1D, FastEthernet0/0
OI FC00:1:1:2001::/64 [110/12]
via FE80::C803:72FF:FE88:1D, FastEthernet0/0
OI FC00:1:1:2011::/64 [110/12]
via FE80::C803:72FF:FE88:1D, FastEthernet0/0
OI FC00:1:1:2021::/64 [110/12]
via FE80::C803:72FF:FE88:1D, FastEthernet0/0
R2#sh ipv6 ospf database | beg Inter Area Prefix Link States
Inter Area Prefix Link States (Area 0)
ADV Router Age Seq# Prefix
10.10.10.10 411 0x80000003 2001::/64
10.10.10.10 88 0x80000001 FC00:1:1:2001::/64
10.10.10.10 78 0x80000001 FC00:1:1:2021::/64
10.10.10.10 78 0x80000001 FC00:1:1:2011::/64
Link (Type-8) Link States (Area 0)
ADV Router Age Seq# Link ID Interface
2.2.2.2 1536 0x80000006 4 Fa0/0
10.10.10.10 411 0x80000008 5 Fa0/0
Intra Area Prefix Link States (Area 0)
ADV Router Age Seq# Link ID Ref-lstype Ref-LSID
2.2.2.2 1536 0x80000006 4096 0x2002 4
To summarized prefix there are two steps:
A) You need to find Summary prefix
B) Configure the "area [area-id] range [IPv6 prefix] [mask] [advertise | not-advertise |cost {cost}]" command under OSPFv3 process:
A) Calculation of Summery prefix:
We have to summarize the following routes:
VLAN 1: FC00:1:1:2001::1/64
VLAN 2: FC00:1:1:2011::1/64
VLAN 3: FC00:1:1:2021::1/64
1) Identify where you can do the summarization. In our example 1st three hexadecimal places are same hence summarization can be done in the 4th hexadecimal place. So we know our subnet will be somewhere between /48 and /64.
2) You need to break it down in binary:
2001= 0010 0000 0000 0001
2011= 0010 0000 0001 0001
2021= 0010 0000 0010 0001
3) Find the common bits then Set the rest bits to 0 and calculate the summary by converting into hex.
2001= 0010 0000 0000 0001
2011= 0010 0000 0001 0001
2021= 0010 0000 0010 0001
Common bits=0010 0000 00
Summary = 0010 0000 0000 0000 = 2000 (In Hex)
4) Calculate subnet mask by adding the common bits to the lower of our subnet range. This means we need to add 10 to /48 which makes /58.
So our summary address is FC00:1:1:2000::/58
B) Configure the area range command On ABR under OSPFv3 process:
ABR#conf t
Enter configuration commands, one per line. End with CNTL/Z.
ABR(config-rtr)#area 1 range FC00:1:1:2000::/58
ABR(config-rtr)#end
ABR#
After configuring summarization on ABR, R2 is receiving only summary route FC00:1:1:2000::/58 not individual type 3 LSA for each VLAN from ABR shown below:
R2#sh ipv6 route ospf
IPv6 Routing Table - 5 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
U - Per-user Static route, M - MIPv6
I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary
O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
D - EIGRP, EX - EIGRP external
OI 2001::/64 [110/11]
via FE80::C803:72FF:FE88:1D, FastEthernet0/0
OI FC00:1:1:2000::/58 [110/12]
via FE80::C803:72FF:FE88:1D, FastEthernet0/0
R2#sh ipv6 ospf database | beg Inter Area Prefix Link States
Inter Area Prefix Link States (Area 0)
ADV Router Age Seq# Prefix
10.10.10.10 578 0x80000004 2001::/64
10.10.10.10 161 0x80000001 FC00:1:1:2000::/58
Link (Type-8) Link States (Area 0)
ADV Router Age Seq# Link ID Interface
2.2.2.2 1707 0x80000007 4 Fa0/0
10.10.10.10 578 0x80000009 5 Fa0/0
Intra Area Prefix Link States (Area 0)
ADV Router Age Seq# Link ID Ref-lstype Ref-LSID
2.2.2.2 1707 0x80000007 4096 0x2002 4
Verifying reachability after summarization from R2:
R2#ping fc00:1:1:2001::1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FC00:1:1:2001::1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/126/192 ms
R2#ping fc00:1:1:2011::1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FC00:1:1:2011::1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/28/44 ms
R2#ping fc00:1:1:2021::1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FC00:1:1:2021::1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/24/52 ms
R2#
Discard Route:
During route summarization, routing loops may occur when data is sent to a non-existing network that appears to be a part of the summary, and the router that is performing the summarization has a less specific route (pointing back to the sending router) for this network in its routing table. To prevent the routing loop, a discard route entry is installed in the routing table of the ABR.
Like in ipv4 after summarization by default ABR generated Discard route pointing towards null0 interface in its routing.
ABR# sh ipv6 route ospf
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, ND - Neighbor Discovery
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
O FC00:1:1:2000::/58 [110/0]
via Null0, directly connected
O FC00:1:1:2001::/64 [110/2]
via FE80::C204:5EFF:FE60:0, FastEthernet1/0
O FC00:1:1:2011::/64 [110/2]
via FE80::C204:5EFF:FE60:0, FastEthernet1/0
O FC00:1:1:2021::/64 [110/2]
via FE80::C204:5EFF:FE60:0, FastEthernet1/0
If you want to disable creation of the discard route, you can use the no discard-route command as follows:
ABR#conf t
Enter configuration commands, one per line. End with CNTL/Z.
ABR(config)#ipv6 router ospf 100
ABR(config-rtr)#no discard-route internal
ABR(config-rtr)#end
ABR# sh ipv6 route ospf
IPv6 Routing Table - default - 7 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, ND - Neighbor Discovery
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
O FC00:1:1:2001::/64 [110/2]
via FE80::C204:5EFF:FE60:0, FastEthernet1/0
O FC00:1:1:2011::/64 [110/2]
via FE80::C204:5EFF:FE60:0, FastEthernet1/0
O FC00:1:1:2021::/64 [110/2]
via FE80::C204:5EFF:FE60:0, FastEthernet1/0
