Cisco – %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link

ciscoospfpacket-tracer

I have a topology like this:

this Router0-1's Gig0/0/0 ip: 10.0.12.1/24,
the Router0-2's Gig0/0/0 ip: 10.0.12.2/24, Gig0/0/1 ip: 10.0.23.2/24,
this Router0-3's Gig0/0/0 ip: 10.0.23.3/24,

at first, all the router interfaces are announced into the Area 0.

now, I announced the Router0-3's Gig0/0/0 and Router0-2's Gig0/0/1 to the Area1, but the Router0-2 get bellow logs:

00:57:06: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 10.0.23.2, GigabitEthernet0/0/1

00:57:16: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 10.0.23.2, GigabitEthernet0/0/1

00:57:26: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 10.0.23.2, GigabitEthernet0/0/1

00:57:36: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 10.0.23.2, GigabitEthernet0/0/1

….

I have tried clear ospf prgress in Router0-3, still this issue.

in the Router0-1 ospf database:

Router1>show ip ospf database 
            OSPF Router with ID (1.1.1.1) (Process ID 1)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
3.3.3.3         3.3.3.3         1703        0x80000002 0x00fef4 1
1.1.1.1         1.1.1.1         1034        0x80000008 0x0071a5 1
2.2.2.2         2.2.2.2         1034        0x80000009 0x0034d7 1

                Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.3       3.3.3.3         1703        0x80000001 0x004c5f
10.0.12.2       2.2.2.2         1034        0x80000002 0x00bd6e

                Summary Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.0       2.2.2.2         1529        0x80000001 0x00d65e
3.3.3.3         2.2.2.2         497         0x80000005 0x00ce76

in the Router0-2 ospf database:

Router2#show ip ospf database 
            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         973         0x80000008 0x0071a5 1
3.3.3.3         3.3.3.3         1642        0x80000002 0x00fef4 1
2.2.2.2         2.2.2.2         973         0x80000009 0x0034d7 1

                Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.3       3.3.3.3         1642        0x80000001 0x004c5f
10.0.12.2       2.2.2.2         973         0x80000002 0x00bd6e

                Summary Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.0       2.2.2.2         1468        0x80000001 0x00d65e
3.3.3.3         2.2.2.2         436         0x80000005 0x00ce76

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         446         0x8000000e 0x0027c8 1
3.3.3.3         3.3.3.3         446         0x80000009 0x00745b 2

                Net Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.3       3.3.3.3         446         0x80000003 0x004ec4

                Summary Net Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.12.0       2.2.2.2         1475        0x80000001 0x0050ef

in the Router0-3 ospf database:

Router3#show  ip ospf database 
            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         536         0x8000000e 0x0027c8 1
3.3.3.3         3.3.3.3         536         0x80000009 0x00745b 2

                Net Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.3       3.3.3.3         536         0x80000003 0x004ec4

                Summary Net Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.12.0       2.2.2.2         1565        0x80000001 0x0050ef

Best Answer

I tried your post experiment, when I in one area to assign R3's interface to Area1, the R2 will get this Error Receive logs.

But if you in R3 no router ospf 1, then launch a new OSPF process, and add the interface to Area 1 there will not get this fault.

and then show the Router2's OSPF database, there shows flawlessly.

Router2#show ip ospf database 
            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         370         0x80000003 0x0048b0 2
1.1.1.1         1.1.1.1         370         0x80000003 0x0055b1 2

                Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.12.2       2.2.2.2         370         0x80000001 0x002f8b

                Summary Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.0       2.2.2.2         365         0x80000001 0x00d65e

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
3.3.3.3         3.3.3.3         375         0x80000003 0x00fef2 1
2.2.2.2         2.2.2.2         275         0x80000005 0x0039bf 1

                Net Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.3       3.3.3.3         275         0x80000002 0x00a032

                Summary Net Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum
3.3.3.3         3.3.3.3         370         0x80000001 0x00ae97
2.2.2.2         2.2.2.2         365         0x80000001 0x00fa53
10.0.12.0       2.2.2.2         365         0x80000002 0x004ef0
1.1.1.1         2.2.2.2         360         0x80000003 0x002f20

OSPF Backbone

Why is area 0 the backbone area in OSPF? Why must all other areas connect to it?

This is explained very well in RFC 3509, Section 1.2¹:

1.2 Motivation

In OSPF domains the area topology is restricted so that there must be a backbone area (area 0) and all other areas must have either physical or virtual connections to the backbone. The reason for this star-like topology is that OSPF inter-area routing uses the distance-vector approach and a strict area hierarchy permits avoidance of the "counting to infinity" problem. OSPF prevents inter-area routing loops by implementing a split-horizon mechanism, allowing ABRs to inject into the backbone only Summary-LSAs derived from the intra-area routes, and limiting ABRs' SPF calculation to consider only Summary-LSAs in the backbone area's link-state database.

OSPF is usually considered a link-state protocol. What some people miss is that OSPF uses both link-state protocol and distance-vector protocol algorithms.

Routes within the backbone, or a non-backbone area are computed as a link-state protocol does (ref Dijkstra's algorithm).
When OSPF must carry non-backbone routes through the backbone, it uses some distance-vector behavior (i.e. parts of the Bellman Ford algorithm) to propagate Type3 LSA metrics into non-backbone areas.

Simple example of OSPF's distance-vector behavior:

<-- Area 5 --><-- Area 0 --><--           Area 4           -->

R5-----------R1-----------R2------------R3---------------------R4
     Cost 3      Cost 5        Cost 7            Cost 12

               LSA-->          LSA-->
               Type3 LSA       Type3 LSA
               {From R1}       {From R2}
               R5 cost is 3    R5 cost is 8

Consider what happens to a /32 Loopback route for R5.

R5 sends a Type1 LSA containing the /32 Loopback
R1 (Area 5 ABR), is connected to Area 0; it translates the Type1 LSA into a Type3 LSA with a cost of 3.
R2 (Area 4 ABR) receives R1's Type3 LSA (metric 3) and changes the metric to R5's Loopback, based on R2's cost to R1. Now R2's Type3 LSA for R5 has a cost of 8. This is the distance-vector behavior I mentioned above.

Requiring all non-backbone routes to go through the backbone is a loop-prevention mechanism.

Connecting non-backbone OSPF areas at an ABR

If 2 areas aren't connected through area 0 (discontiguous), how does OSPF behaving as a link state protocol increase the possibility of routing loops?

As we saw above, OSPF uses distance-vector behavior to send routes through the Area 0 backbone. Distance-vector protocols have well-known limits, such as the count-to-infinity problem. OSPF would be vulnerable to the same issues, if we didn't have boundaries on its behavior.

¹_{RFC 3509 describes Cisco IOS's ABR behavior}

Best Answer

Related Solutions

Cisco – OSPF Area Backbone(0) is Inactive

OSPF Routing – Why Must All Areas Connect to Area 0 Backbone?

OSPF Backbone

Connecting non-backbone OSPF areas at an ABR

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