topic Re: Route map with continue clause in Routing and SD-WAN

Route map with continue clause

verma-rohit — Mon, 27 Jul 2020 06:32:18 GMT

Hello,

I was experimenting with route-map with continue clause, however the use of continue clause does not set well with my understanding of its processing.

1. A route matches a match statement execute its configured set values and then jumps to other sequence number as per configured continue statement.

2. If next route-map sequence has no match statement, it should execute configured set action.

1. Access and Core are OSPF neighbors.

2. On Core:

Core#show ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.0.6       1   FULL/DR         00:00:39    10.0.128.2      GigabitEthernet0/2
Core#show ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      192.168.0.0/32 is subnetted, 3 subnets
O        192.168.0.6 [110/2] via 10.0.128.2, 00:39:07, GigabitEthernet0/2
O E2  192.168.1.0/24 [110/20] via 10.0.128.2, 00:39:07, GigabitEthernet0/2
      192.168.2.0/32 is subnetted, 1 subnets
O E2     192.168.2.1 [110/20] via 10.0.128.2, 00:39:07, GigabitEthernet0/2
Core#
Core#

3. On Same Core, I have BGP configured to perform OSPF route redistribution:

OSPF route on Core with TAG 2001
Core#show ip route 192.168.2.1
Routing entry for 192.168.2.1/32
  Known via "ospf 64501", distance 110, metric 20
  Tag 2001, type extern 2, forward metric 1
  Redistributing via bgp 64501
  Advertised by bgp 64501 route-map OSPF2BGP
  Last update from 10.0.128.2 on GigabitEthernet0/2, 00:50:55 ago
  Routing Descriptor Blocks:
  * 10.0.128.2, from 192.168.0.6, 00:50:55 ago, via GigabitEthernet0/2
      Route metric is 20, traffic share count is 1
      Route tag 2001

Core#sh run | s r b
router bgp 64501
 bgp router-id 192.168.0.5
 bgp log-neighbor-changes
 neighbor 10.0.0.2 remote-as 65001
 neighbor 10.0.0.2 description Client
 neighbor 10.0.0.5 remote-as 64500
 neighbor 10.0.0.5 description eBGP to Upstream
 !
 address-family ipv4
  network 10.0.0.0 mask 255.255.0.0
  network 192.168.0.5 mask 255.255.255.255
  redistribute ospf 64501 route-map OSPF2BGP
  neighbor 10.0.0.2 activate
  neighbor 10.0.0.2 send-community
  neighbor 10.0.0.2 next-hop-self
  neighbor 10.0.0.2 route-map FromClient in
  neighbor 10.0.0.5 activate
  neighbor 10.0.0.5 send-community
  neighbor 10.0.0.5 next-hop-self
 exit-address-family
Core#

4. Route-map on Core

Core#show route-map OSPF2BGP
route-map OSPF2BGP, permit, sequence 10
  Match clauses:
    route-type external 
     tag 2000 
  Continue: to next entry 11
  Set clauses:
    community 64501:2 additive
    origin egp 64501
  Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 11
  Match clauses:
    route-type external 
  Continue: to next entry 20
  Set clauses:
    community 64501:2001 additive
    origin igp
  Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 20
  Match clauses:
  Set clauses:
    weight 200
  Policy routing matches: 0 packets, 0 bytes
Core#

Result:

On core, I anticipated BGP attributes for route 192.168.2.1 to have:

1. community 64501:2001 and origin as IGP

2. As there is continue configured on in seq 11, control moves to seq 20 and assign weight 200.

However , seq 20 is never executed it seems. Any reason why ?

Core#show ip bgp 192.168.2.1
BGP routing table entry for 192.168.2.1/32, version 8
Paths: (1 available, best #1, table default)
  Advertised to update-groups:
     4         
  Refresh Epoch 1
  Local
    10.0.128.2 from 0.0.0.0 (192.168.0.5)
      Origin IGP, metric 20, localpref 100, weight 32768, valid, sourced, best
      Community: 64501:2001
      rx pathid: 0, tx pathid: 0x0

Re: Route map with continue clause

verma-rohit — Mon, 27 Jul 2020 06:33:02 GMT

Please ignore spoiler tag

Re: Route map with continue clause

Georg Pauwen — Mon, 27 Jul 2020 07:13:50 GMT

Hello,

at first glance, I would say your match clauses in sequence 10 and 11 don't match, so 12 is never executed:

Core#show route-map OSPF2BGP
route-map OSPF2BGP, permit, sequence 10
Match clauses:
route-type external
tag 2000
Continue: to next entry 11
Set clauses:
community 64501:2 additive
origin egp 64501
Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 11
Match clauses:
route-type external
Continue: to next entry 20
Set clauses:
community 64501:2001 additive
origin igp
Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 20
Match clauses:
Set clauses:
weight 200
Policy routing matches: 0 packets, 0 bytes
Core#

Add the same tag to sequence 11:

--> tag 2000
Continue: to next entry 20
Set clauses:
community 64501:2001 additive
origin igp
Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 20
Match clauses:
Set clauses:
weight 200
Policy routing matches: 0 packets, 0 bytes
Core#

Re: Route map with continue clause

verma-rohit — Mon, 27 Jul 2020 07:30:01 GMT

Hi,

Thanks for your feedback.

Well seq 11 did match because the said route is an external ( E2 ) route and as a result community 64501:2001 and origin was set as IGP.

Re: Route map with continue clause

Georg Pauwen — Mon, 27 Jul 2020 08:35:39 GMT

Hello,

what if you match sequence 20 as well ? I think the logic is that the match statements have to be the same for each sequence if you use the 'continue' but everything else that does NOT match the previous will get the weight you configured.

Core#show route-map OSPF2BGP
route-map OSPF2BGP, permit, sequence 10
Match clauses:
route-type external
tag 2000
Continue: to next entry 11
Set clauses:
community 64501:2 additive
origin egp 64501
Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 11
Match clauses:
route-type external
Continue: to next entry 20
Set clauses:
community 64501:2001 additive
origin igp
Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 20Match clauses:

--> route-type external

Set clauses:
weight 200
Policy routing matches: 0 packets, 0 bytes
Core#

Re: Route map with continue clause

verma-rohit — Mon, 27 Jul 2020 10:00:03 GMT

Hi,

I did add match clause in seq 20, however weight is still unchanged.

Core#show route-map OSPF2BGP
route-map OSPF2BGP, permit, sequence 10
  Match clauses:
    route-type external 
     tag 2000 
  Continue: to next entry 11
  Set clauses:
    community 64501:2 additive
    origin egp 64501
  Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 11
  Match clauses:
    route-type external 
  Continue: to next entry 20
  Set clauses:
    community 64501:2001 additive
    origin igp
  Policy routing matches: 0 packets, 0 bytes
route-map OSPF2BGP, permit, sequence 20
  Match clauses:
    route-type external 
  Set clauses:
    weight 200
  Policy routing matches: 0 packets, 0 bytes
Core#

Core#show ip route 192.168.2.1
Routing entry for 192.168.2.1/32
  Known via "ospf 64501", distance 110, metric 20
  Tag 2001, type extern 2, forward metric 1
  Redistributing via bgp 64501
  Advertised by bgp 64501 route-map OSPF2BGP
  Last update from 10.0.128.2 on GigabitEthernet0/2, 00:35:47 ago
  Routing Descriptor Blocks:
  * 10.0.128.2, from 192.168.0.6, 00:35:47 ago, via GigabitEthernet0/2
      Route metric is 20, traffic share count is 1
      Route tag 2001

Core#show ip bgp 192.168.2.1
BGP routing table entry for 192.168.2.1/32, version 6
Paths: (1 available, best #1, table default)
  Advertised to update-groups:
     2         
  Refresh Epoch 1
  Local
    10.0.128.2 from 0.0.0.0 (192.168.0.5)
      Origin IGP, metric 20, localpref 100, weight 32768, valid, sourced, best
      Community: 64501:2001
      rx pathid: 0, tx pathid: 0x0

Re: Route map with continue clause

Georg Pauwen — Mon, 27 Jul 2020 10:58:47 GMT

Hello,

I'll try to lab this...can you post the full running configs of both the access and the core router ?

Re: Route map with continue clause

paul driver — Mon, 27 Jul 2020 11:28:57 GMT

Hello

@verma-rohit wrote:

Hello,

2. If next route-map sequence has no match statement, it should execute configured set action.

FYI - TAGs don’t work with route-map redistribution into bgp, Communities are the equivalent.
As the match clause in stanza 10 was on external routes and the tags are not applicable then the router will just read the match clause which basically has no set statement.
I would assume the continue 11 will work however there isn't anything else to match upon because this was performed in stanza 10, if you tried to match on another prefix that isnt in the first match from stanza 10 then it should read stanza 11 but at this time there isn’t any else to match on .

Try the following and see if the community 64501:2 works for 192.168.2.0/24

neighbor 10.0.0.2 send-community both
neighbor 10.0.0.5 send-community both

ip prefix-list 10 permit 192.168.1.0/24

route-map OSPF2BGP permit 10
match ip address prefix-list 10
continue 11
set tag 2000 < …………. doesnt work

route-map OSPF2BGP permit 11
set community 64501:2 additive

Re: Route map with continue clause

verma-rohit — Mon, 27 Jul 2020 11:45:59 GMT

Hi,

Files are attached , Shared below is the topology.

Re: Route map with continue clause

verma-rohit — Mon, 27 Jul 2020 12:01:04 GMT

Hi Paul,

Thanks for your feedback.

FYI - TAGs don’t work with route-map redistribution into bgp, Communities are the equivalent.

I have another E2 route on Core , 192.168.1.0 with a TAG of 2000 and it matched seq 10 for redistributed into BGP.

Core#show ip route 192.168.1.0
Routing entry for 192.168.1.0/24
  Known via "ospf 64501", distance 110, metric 20
  Tag 2000, type extern 2, forward metric 1
  Redistributing via bgp 64501
  Advertised by bgp 64501 route-map OSPF2BGP
  Last update from 10.0.128.2 on GigabitEthernet0/2, 02:29:26 ago
  Routing Descriptor Blocks:
  * 10.0.128.2, from 192.168.0.6, 02:29:26 ago, via GigabitEthernet0/2
      Route metric is 20, traffic share count is 1
      Route tag 2000

Core#
Core#show run | sec OSPF2BGP
  redistribute ospf 64501 route-map OSPF2BGP
route-map OSPF2BGP permit 10
 match tag 2000
 match route-type external
 continue
 set origin egp 64501
 set community 64501:2 additive
route-map OSPF2BGP permit 11
 match route-type external
 continue
 set origin igp
 set community 64501:2001 additive
route-map OSPF2BGP permit 20
 match route-type external
 set weight 200
Core#


Core#show ip bgp 192.168.1.0
BGP routing table entry for 192.168.1.0/24, version 6
Paths: (1 available, best #1, table default)
  Advertised to update-groups:
     5         
  Refresh Epoch 1
  Local
    10.0.128.2 from 0.0.0.0 (192.168.0.5)
      Origin EGP, metric 20, localpref 100, weight 32768, valid, sourced, best
      Community: 64501:2
      rx pathid: 0, tx pathid: 0x0

Now continue in Seq 10 would allowed Seq 11 to execute as well and based on text which i shared in initial post, should have overwritten origin code and community value but it wasn't to be.

I will test the script which you asked me to configure and share my feedback.

Re: Route map with continue clause

Georg Pauwen — Mon, 27 Jul 2020 13:33:58 GMT

I'll lab this up...thanks for the files.

Re: Route map with continue clause

paul driver — Tue, 28 Jul 2020 09:16:51 GMT

Hello
I could have made myself a bit clearer, You can match on a tagged ospf prefix that is to be redistributed into bgp but setting a tag then this wont work, And ive just realized you are indeed matching on a tag so my mistake, So referring back to your own OP for route-map stanza 11 ,the resulting logic would be the external ospf prefix 192.168.2.0 /24 with a tag 2001 should be set an origin IGB with a community PA of 64501:2001 which looks correct from your OP post.

10.0.128.2 from 0.0.0.0 (192.168.0.5)
Origin IGP, metric 20, localpref 100, weight 32768, valid, sourced, best
Community: 64501:2001

The reason for this would be that in stanza 10 a match is made on both external routes and tag of 2000 for 192.168.1.0/24 but not 192.168.2.0/24 then the continue is adhered in stanza 11(next stanza as no number is specified) where again a match is made on specifically any external routes that was not matched in the previous stanza and by time you get to the last stanza 20 all of the external routes have already been matched but with the continue the set command should be applied.

Re: Route map with continue clause

Georg Pauwen — Mon, 27 Jul 2020 19:58:48 GMT

Hello,

I ran into the same issue you had. For some reason, the 'continue' statement does not seem to work in route maps that are used in redistribution of routing protocols. The only way I got this to work is with the route map below (the 'additive' obviously is redundant). I did come across a document though that mirrors your setup. I am not sure if this is VIRL specific, and if the 'continue' clause works in e.g. XE.

Have a look at what this user noticed:

BGP Route Maps and Continue Feature Limitations

https://blog.ipspace.net/2016/05/bgp-route-maps-and-continue-feature.html

route-map OSPF2BGP permit 10
match tag 2000
match route-type external
set origin egp 64501
set community 64501:2 additive
!
route-map OSPF2BGP permit 11
match route-type external
set origin igp
set community 64501:2001 additive
!
route-map OSPF2BGP permit 11
match route-type external
set weight 200

Re: Route map with continue clause

verma-rohit — Tue, 28 Jul 2020 00:50:28 GMT

Hello,

I have gone through the shared link. From the website:

The lack of support for continue clause was somewhat expected after reading the relevant IOS documentation, and without the continue clause it makes no sense using set community additive in a redistribution point (where source routes have no BGP communities).

Link: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/15-mt/irg-15-mt-book/irg-route-map-continue.html

Where exactly in shared link author talsk about " lack of support for continue clause" ?

Re: Route map with continue clause

Giuseppe Larosa — Tue, 28 Jul 2020 06:25:18 GMT

Hello @verma-rohit ,

all the configuration examples in the shared link show route-maps applied to BGP neighbor statements for this use case the route-map continue command has been introduced and supported.

The continue command is not supported in route-maps used for redistribution like in your tests and in the tests performed in the blog mentioned by Georg.

Hope to help

Giuseppe

Re: Route map with continue clause

paul driver — Tue, 28 Jul 2020 09:19:30 GMT

Hello

@Giuseppe Larosa wrote:

The continue command is not supported in route-maps used for redistribution

I manage to test this last night and TBH it wasnt soemthing i was aware of, you would think it would be documented regards its restriction with redistribution or is this be something cisco will expect us to logically take into account

3700 Software (C3725-ADVENTERPRISEK9-M), Version 12.4(15)T14
7200 Software (C7200-ADVENTERPRISEK9-M), Version 15.2(4)M11, RELEASE SOFTWARE (fc2
IOSv Software (VIOS-ADVENTERPRISEK9-M), Version 15.8(3)M2, RELEASE SOFTWARE (fc2
Cisco IOS Software [Fuji], Virtual XE Software (X86_64_LINUX_IOSD-UNIVERSALK9-M), Version 16.9.1, RELEASE SOFTWARE (fc2)

% "TST" used as redistribute ospf into bgp route-map, continue match not supported
% not supported match will behave as route-map with no match
% "TST" used as redistribute ospf into bgp route-map, set community add not supported

Re: Route map with continue clause

Giuseppe Larosa — Tue, 28 Jul 2020 09:32:05 GMT

Hello @paul driver ,

your test results are exactly the same as those shown in the link

https://blog.ipspace.net/2016/05/bgp-route-maps-and-continue-feature.html

by Ivan Pepelnjack

this link was found by @Georg Pauwen and reported in this thread. The source is rather reliable.

About the continue statement I remember it was introduced for BGP only.

There was another recent thread where the OP tried to use the continue in a route map used to redistribute into EIGRP wth no success.

In my humble opinion the OP of this thread is actually repeating the lab setup reported in that blog page with same results.

Hope to help

Giuseppe

Re: Route map with continue clause

paul driver — Tue, 28 Jul 2020 10:29:04 GMT

@Giuseppe Larosa

I don’t doubt the source isn’t viable mate especially coming from the likes Ivan it’s just quite frustrating isn’t documented and I wasn’t aware this OP was plagiarized from IVAN post.

Anyway all good I have learnt something this morning I didn’t know last night!

Re: Route map with continue clause

Georg Pauwen — Tue, 28 Jul 2020 10:36:12 GMT

I agree with Paul and Giuseppe. Nowhere is this documented, so you kind of have to conclude that it doesn't work in redistribution just by trial and error. I have spent a good amount of time searching but could not find a single mention of this restriction anywhere...

The good thing is: now we know !

How would one proceed to get Cisco to include this in the documentation ?