[quagga-dev 16613] Re: [quagga-users 14675] Potential problem in rib_process function

[Balaji Gurudoss]

Ideally speaking the implicit withdraw would happen when the new one gets
selected and old one gets validated. Are you seeing this issue with a very
simple topology with two routers connected back to back running OSPF or do
you see it in a specific topology ?

Thanks,
- Balaji

Hi Guys,
I am using quagga release 1.2.1. I see one potential problem in
rib_process function related to withdrawal of redistributed route from
zebra.
Problematic line is marked in bold letters.
Suppose a prefix was already learned via OSPF. Now if I try to add a
static route for same prefix, I hit this code.
In this case. old_selected will point to OSPF and new_selected will point
to Static. Now since ospf route is not the selected one, don;t we
always have to withdraw this ospf route from clients redistributing OSPF.
Why there is extra check there ?
I also tested this locally. If I comment this if statement then I see
zebra sending delete for OSPF route else not.
Pls give advice.
Rgds
Atul
/* Redistribute SELECTED entry */
1308 if (old_selected != new_selected
1309 || (new_selected && CHECK_FLAG (new_selected->status,
RIB_ENTRY_CHANGED)))
1310 {
1311 if (old_selected)
1312 {
1313 * if (! new_selected) >>>> Why this if statement is
there ?? I fell this shouldn't be there.*
1314 redistribute_delete (&rn->p, old_selected);
1315 if (old_selected != new_selected)
1316 UNSET_FLAG (old_selected->flags, ZEBRA_FLAG_SELECTED);
1317 }
1318
1319 if (new_selected)
1320 {
1321 /* Install new or replace existing redistributed entry */
1322 SET_FLAG (new_selected->flags, ZEBRA_FLAG_SELECTED);
1323 redistribute_add (&rn->p, new_selected);
1324 }
1325 }
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[Balaji Gurudoss]

Hi Atul

This would happen with any protocol and not with ospf because this is an
expected behaviour. I believe the following is what you are looking at

Router A-----Router B

You have configured a static route in Router B and are doing a redistribute
static into OSPF/BGP in Router B. The show ip route on Router B would show
the route as a BGP/OSPF learned route. Now on router B you configure a
static route with the same prefix pointing to a next-hop and in RTM the
newly created static route would be marked as the Best route instead of BGP
as the static route has more preference.

Now as per BGP/OSPF is concerned, 50.1.1.0/24 is still the best route on
the router where the route was originated i.e Router B. On router A it
isn't the best route because a static route for the same prefix has been
created. In this scenario why should Router B withdraw the route ? How
would router B know that there is a static route existing in Router A for
the same destination ?

Hope you get my point.

Thanks,
- Balaji

Hi Balaji,
What do you mean when you say implicit withdraw ? I am seeing this in
very simple topology of two routers running ospf and connected back to back.
Rgds
Atul

Post by Balaji Gurudoss
Ideally speaking the implicit withdraw would happen when the new one gets
selected and old one gets validated. Are you seeing this issue with a very
simple topology with two routers connected back to back running OSPF or do
you see it in a specific topology ?
Thanks,
- Balaji

Hi Guys,
I am using quagga release 1.2.1. I see one potential problem in
rib_process function related to withdrawal of redistributed route from
zebra.
Problematic line is marked in bold letters.
Suppose a prefix was already learned via OSPF. Now if I try to add a
static route for same prefix, I hit this code.
In this case. old_selected will point to OSPF and new_selected will
point to Static. Now since ospf route is not the selected one, don;t we
always have to withdraw this ospf route from clients redistributing
OSPF. Why there is extra check there ?
I also tested this locally. If I comment this if statement then I see
zebra sending delete for OSPF route else not.
Pls give advice.
Rgds
Atul
/* Redistribute SELECTED entry */
1308 if (old_selected != new_selected
1309 || (new_selected && CHECK_FLAG (new_selected->status,
RIB_ENTRY_CHANGED)))
1310 {
1311 if (old_selected)
1312 {
1313 * if (! new_selected) >>>> Why this if statement is
there ?? I fell this shouldn't be there.*
1314 redistribute_delete (&rn->p, old_selected);
1315 if (old_selected != new_selected)
1316 UNSET_FLAG (old_selected->flags, ZEBRA_FLAG_SELECTED);
1317 }
1318
1319 if (new_selected)
1320 {
1321 /* Install new or replace existing redistributed entry */
1322 SET_FLAG (new_selected->flags, ZEBRA_FLAG_SELECTED);
1323 redistribute_add (&rn->p, new_selected);
1324 }
1325 }
_______________________________________________
Quagga-users mailing list
https://lists.quagga.net/mailman/listinfo/quagga-users

[Balaji Gurudoss]

Hi Atul

My example also is about configuring static route on the same box where the
route is learned as an OSPF route.

Can you let me know if my understanding below is right

Router A--------Router B

1.Router B has a static route configured (eg: 50.1.1.0/24 10.1.1.50)
2. Router B has redistribute static configured
3. There is OSPF/BGP session configured between Router A and Router B
4. On Router A the prefix 50.1.1.0/24 would be shown as an OSPF/BGP learned
route
5. On Router A a static route pointing to 50.1.1.0/24 is now configured
with a different next-hop.
6. On Router A, the static route is displayed as the best route instead of
the OSPF route because of lesser administrative distance for static route.

Now in the above mentioned scenario, what is your expectation and whats
your question

Thanks,
- Balaji

Hi Balaji,
May be I am missing something but I am talking about both static and OSPF
route on same router. In ur example, Its assuming that static route is
added on Router B rather than A.
Any other quagga Guru, who can pls clarify my query here ?
Rgds
Atul

Post by Balaji Gurudoss
Hi Atul
This would happen with any protocol and not with ospf because this is an
expected behaviour. I believe the following is what you are looking at
Router A-----Router B
You have configured a static route in Router B and are doing a
redistribute static into OSPF/BGP in Router B. The show ip route on Router
B would show the route as a BGP/OSPF learned route. Now on router B you
configure a static route with the same prefix pointing to a next-hop and in
RTM the newly created static route would be marked as the Best route
instead of BGP as the static route has more preference.
Now as per BGP/OSPF is concerned, 50.1.1.0/24 is still the best route
on the router where the route was originated i.e Router B. On router A it
isn't the best route because a static route for the same prefix has been
created. In this scenario why should Router B withdraw the route ? How
would router B know that there is a static route existing in Router A for
the same destination ?
Hope you get my point.
Thanks,
- Balaji

Hi Balaji,
What do you mean when you say implicit withdraw ? I am seeing this in
very simple topology of two routers running ospf and connected back to back.
Rgds
Atul

Post by Balaji Gurudoss
Ideally speaking the implicit withdraw would happen when the new one
gets selected and old one gets validated. Are you seeing this issue with a
very simple topology with two routers connected back to back running OSPF
or do you see it in a specific topology ?
Thanks,
- Balaji

Hi Guys,
I am using quagga release 1.2.1. I see one potential problem in
rib_process function related to withdrawal of redistributed route from
zebra.
Problematic line is marked in bold letters.
Suppose a prefix was already learned via OSPF. Now if I try to add a
static route for same prefix, I hit this code.
In this case. old_selected will point to OSPF and new_selected will
point to Static. Now since ospf route is not the selected one, don;t we
always have to withdraw this ospf route from clients redistributing
OSPF. Why there is extra check there ?
I also tested this locally. If I comment this if statement then I see
zebra sending delete for OSPF route else not.
Pls give advice.
Rgds
Atul
/* Redistribute SELECTED entry */
1308 if (old_selected != new_selected
1309 || (new_selected && CHECK_FLAG (new_selected->status,
RIB_ENTRY_CHANGED)))
1310 {
1311 if (old_selected)
1312 {
1313 * if (! new_selected) >>>> Why this if statement
is there ?? I fell this shouldn't be there.*
1314 redistribute_delete (&rn->p, old_selected);
1315 if (old_selected != new_selected)
1316 UNSET_FLAG (old_selected->flags, ZEBRA_FLAG_SELECTED);
1317 }
1318
1319 if (new_selected)
1320 {
1321 /* Install new or replace existing redistributed entry */
1322 SET_FLAG (new_selected->flags, ZEBRA_FLAG_SELECTED);
1323 redistribute_add (&rn->p, new_selected);
1324 }
1325 }
_______________________________________________
Quagga-users mailing list
https://lists.quagga.net/mailman/listinfo/quagga-users

[Balaji Gurudoss]

Hi Atul

i get your point. This looks like an issue. It does not make sense to have
that route on the peer. This route should be withdrawn from Router B as the
OSPF route is no more the best route. Can you open a bug for this in
bugzilla.quagga.net

Thanks,
- Balaji

Hi Balaji,
Router A--------Router B---------Router C
Lets say Router B and C have an RIP session and Router A and B have OSPF
session. Router B's RIP is redistributing OSPF.
Router B learns 50.1.1.0/24 route from Router A through OSPF and
redistributes that route to Router C.
Now On Router B, user configures a static route with same prefix (
50.1.1.0/24). This static route on router B will be chosen as best route because
of lesser administrative distance.
Now question is Doesn't Router B withdraw its earlier distributed OSPF
route (50.1.1.0/24) from Router C ?
Rgds
Atul

Post by Balaji Gurudoss
Hi Atul
My example also is about configuring static route on the same box where
the route is learned as an OSPF route.
Can you let me know if my understanding below is right
Router A--------Router B
1.Router B has a static route configured (eg: 50.1.1.0/24 10.1.1.50)
2. Router B has redistribute static configured
3. There is OSPF/BGP session configured between Router A and Router B
4. On Router A the prefix 50.1.1.0/24 would be shown as an OSPF/BGP
learned route
5. On Router A a static route pointing to 50.1.1.0/24 is now configured
with a different next-hop.
6. On Router A, the static route is displayed as the best route instead
of the OSPF route because of lesser administrative distance for static
route.
Now in the above mentioned scenario, what is your expectation and whats
your question
Thanks,
- Balaji

Hi Balaji,
May be I am missing something but I am talking about both static and
OSPF route on same router. In ur example, Its assuming that static route is
added on Router B rather than A.
Any other quagga Guru, who can pls clarify my query here ?
Rgds
Atul

Post by Balaji Gurudoss
Hi Atul
This would happen with any protocol and not with ospf because this is
an expected behaviour. I believe the following is what you are looking at
Router A-----Router B
You have configured a static route in Router B and are doing a
redistribute static into OSPF/BGP in Router B. The show ip route on Router
B would show the route as a BGP/OSPF learned route. Now on router B you
configure a static route with the same prefix pointing to a next-hop and in
RTM the newly created static route would be marked as the Best route
instead of BGP as the static route has more preference.
Now as per BGP/OSPF is concerned, 50.1.1.0/24 is still the best route
on the router where the route was originated i.e Router B. On router A it
isn't the best route because a static route for the same prefix has been
created. In this scenario why should Router B withdraw the route ? How
would router B know that there is a static route existing in Router A for
the same destination ?
Hope you get my point.
Thanks,
- Balaji

Hi Balaji,
What do you mean when you say implicit withdraw ? I am seeing this in
very simple topology of two routers running ospf and connected back to back.
Rgds
Atul

Post by Balaji Gurudoss
Ideally speaking the implicit withdraw would happen when the new one
gets selected and old one gets validated. Are you seeing this issue with a
very simple topology with two routers connected back to back running OSPF
or do you see it in a specific topology ?
Thanks,
- Balaji

Hi Guys,
I am using quagga release 1.2.1. I see one potential problem in
rib_process function related to withdrawal of redistributed route from
zebra.
Problematic line is marked in bold letters.
Suppose a prefix was already learned via OSPF. Now if I try to add a
static route for same prefix, I hit this code.
In this case. old_selected will point to OSPF and new_selected will
point to Static. Now since ospf route is not the selected one, don;t we
always have to withdraw this ospf route from clients redistributing
OSPF. Why there is extra check there ?
I also tested this locally. If I comment this if statement then I
see zebra sending delete for OSPF route else not.
Pls give advice.
Rgds
Atul
/* Redistribute SELECTED entry */
1308 if (old_selected != new_selected
1309 || (new_selected && CHECK_FLAG (new_selected->status,
RIB_ENTRY_CHANGED)))
1310 {
1311 if (old_selected)
1312 {
1313 * if (! new_selected) >>>> Why this if
statement is there ?? I fell this shouldn't be there.*
1314 redistribute_delete (&rn->p, old_selected);
1315 if (old_selected != new_selected)
1316 UNSET_FLAG (old_selected->flags,
ZEBRA_FLAG_SELECTED);
1317 }
1318
1319 if (new_selected)
1320 {
1321 /* Install new or replace existing redistributed entry */
1322 SET_FLAG (new_selected->flags, ZEBRA_FLAG_SELECTED);
1323 redistribute_add (&rn->p, new_selected);
1324 }
1325 }
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Quagga-users mailing list
https://lists.quagga.net/mailman/listinfo/quagga-users