OSPF: Incorrect RFC2328 implementation: lost default

[dl001]

Description

Accepting an external route (default) and router (ASBR-Summary) via RFC2328 (without compatible RFC1583) wrongly programmed.

When the number of Areas is more than 1, the External routes is selected solely based on the not BackBone area (Area 0). The priority route should be chosen from the no BackBone, but in case of failure, it should be used from the BackBone. This is not happening.

I am attaching the correction patch below.

Version

All version!

# show version
FRRouting 10.5.0 (m9.rmt.ru) on FreeBSD(12.3-STABLE).
Copyright 1996-2005 Kunihiro Ishiguro, et al.
configured with:
    '--prefix=/usr/local/frr-10.5.0' '--localstatedir=/usr/local/frr-10.5.0/var' '--disable-doc' '--enable-multipath=0' '--enable-configfile-mask=0640' '--enable-logfile-mask=0640' '--enable-rpki' '--enable-vty-group=frrvty' '--with-vtysh-pager=more -e' '--enable-protobuf' 'PKG_CONFIG_PATH=/usr/libdata/pkgconfig:/usr/local/protobuf-21.12/lib/pkgconfig:/usr/local/protobuf-c-1.4.1/lib/pkgconfig:/usr/local/libyang-3.7.8/lib/pkgconfig:/usr/local/pcre2-10.40/lib/pkgconfig:/usr/local/rtrlib-0.8.0/lib/pkgconfig' 'CFLAGS=-pipe -g' 'LDFLAGS=-L/usr/local/gettext-0.19.8.1/lib -L/usr/local/readline-8.0/lib -lcurses -L/usr/local/json-c-0.14-20200419/lib -L/usr/local/libyang-3.7.8/lib' 'CPPFLAGS=-I/usr/local/gettext-0.19.8.1/include -I/usr/local/readline-8.0/include -I/usr/local/json-c-0.14-20200419/include -I/usr/local/rtrlib-0.8.0/include/ -I/usr/local/libyang-3.7.8/include/ -I/usr/local/protobuf-c-1.4.1/include/'

How to reproduce

Two routers with parallel areas (BackBone + stub). BackBone not proirity cost. Redistribute the external route on the one router.

Expected behavior

The priority route should be chosen from the no BackBone, but in case of failure, it should be used from the BackBone.

Actual behavior

On the second router, the route is in the OSPF database (sh ip ospf da exter), but not in the route table (sh ip ospf
route).

Have default:

sh ip ospf database external 0.0.0.0

       OSPF Router with ID (10.169.240.56)

                AS External Link States

  LS age: 1167
  Options: 0x20 : *|-|DC|-|-|-|-|-
  LS Flags: 0x6
  LS Type: AS-external-LSA
  Link State ID: 0.0.0.0 (External Network Number)
  Advertising Router: 10.169.240.2
  LS Seq Number: 800025b8
  Checksum: 0xc6c0
  Length: 36

  Network Mask: /0
        Metric Type: 2 (Larger than any link state path)
        TOS: 0
        Metric: 1
        Forward Address: 0.0.0.0
        External Route Tag: 5523

With compatible RFC1583 - have route in RIB table

sh ip ospf route
============ OSPF external routing table ===========
N E2 0.0.0.0/0             [101/1] tag: 5523
                           via 10.169.182.2, vlan3921

Without compatible RFC1583 - There is no route in RIB table.

Additional context

The patch solves the problem

frr-10.5.0.RFC2328_ASE.patch

Checklist

• I have searched the open issues for this bug.
• I have not included sensitive information in this report.

[Ko496-glitch]

@dl001 hey i will try to reproduce error and work on this

[Ko496-glitch]

@dl001 from my understanding if we have multiple paths to asbr and if link fails instead of falling back to backbone route we dont install route to rib

[dl001]

Not multiple paths - multilpe Areas (of course with multiple networks).

Example

sh ip ospf border-routers
R    10.169.240.3          [100] area: 0.0.0.1, ABR
                           via 10.168.182.3, vlan3927
                           [100] area: 0.0.0.0, ABR, ASBR
                           via 10.169.182.3, vlan3921
R    10.169.240.16         [110] area: 0.0.0.1, ABR
                           via 10.168.182.3, vlan3927
                           [101] area: 0.0.0.0, ABR, ASBR
                           via 10.169.182.22, vlan3921

 sh ip ospf database external 0.0.0.0
       OSPF Router with ID (10.169.240.93)
                AS External Link States
  LS Type: AS-external-LSA
  Link State ID: 0.0.0.0 (External Network Number)
  Advertising Router: 10.169.240.3

  LS Type: AS-external-LSA
  Link State ID: 0.0.0.0 (External Network Number)
  Advertising Router: 10.169.240.16

With COMAPTIBLE 1583 default is set to 10.168.182.3 for RR 10.169.240.3 .

Without COMAPTIBLE 1583 default is not set because analyse only area: 0.0.0.1 . This is incorrect behavior. There must be a second choice - 10.169.182.3 for area 0.0.0.0 .

If you have reviewed the patch, then there is not only the choice of default's need a second chance, but also the announcement of asbr-summary .

[Ko496-glitch]

@dl001 correct, asbr announcement completely slipped from my brain. The patch from my perspective looks good. I am a contributor too so try to open a pr and lets see what maintainer says :), but solid fix tho !