Missing IPv4 routes

Missing IPv4 routes

[Brian Rak]

I've got a weird situation here.  I have a route that the kernel knows 
about, but won't display via the general RTM_GETROUTE call, but will 
display if I query for that particular route:

# ip -4 route show | grep 108.61.171.x
# ip route get 108.61.171.x
108.61.171.x dev MYIF
     cache
# cat /proc/net/route | grep 108.61.171.x
#
# cat /proc/net/route  | grep -i 6c3dac
#
# ip route add 108.61.171.x dev MYIF
RTNETLINK answers: File exists
# ip route del 108.61.171.x  <---- it deletes successfully once
# ip route del 108.61.171.x
RTNETLINK answers: No such process


This is on a machine running 4.1.3, but I have seen it on earlier 
versions in the past.

I don't have great reproduction steps here, I've seen this 4-5 times in 
the past few months (on different hardware).  So far, I haven't really 
found any way of fixing it (deleting and readding the route has no 
effect).  I thought at first this might be related to 
e55ffaf457bcc8ec4e9d9f56f955971f834d65b3, but as far as I can tell that 
only relates to /proc/net/route.

Any suggestions on further troubleshooting here?  I'm all out of ideas 
(and since I can't easily reproduce it yet, I can't reboot to a newer 
kernel to see if it goes away)

Re: Missing IPv4 routes

[Alexander Duyck]

On 10/23/2015 02:34 PM, Brian Rak wrote:
> I've got a weird situation here.  I have a route that the kernel knows
> about, but won't display via the general RTM_GETROUTE call, but will
> display if I query for that particular route:
>
> # ip -4 route show | grep 108.61.171.x

The use of 'x' here is going to make things confusing.  I assume you are 
using a value of 0 here, or is this a route to a specific IP address 
that you have.  If not you should be using a 0 for all bits that would 
be outside of your subnet mask.

> # ip route get 108.61.171.x
> 108.61.171.x dev MYIF
>      cache

The 'x' being the actual value here should work as this will perform a 
lookup as I recall.

> # cat /proc/net/route | grep 108.61.171.x

The IPs are in network order and as just hex so this won't work.

> # cat /proc/net/route  | grep -i 6c3dac

The byte ordering you are using is backwards here from what I can tell. 
  So it should be ac3d6c you are checking for, not the other way around. 
  So for example if I was using 192.168.1.x I would want to look for 01A8C0.

> # ip route add 108.61.171.x dev MYIF
> RTNETLINK answers: File exists
> # ip route del 108.61.171.x  <---- it deletes successfully once
> # ip route del 108.61.171.x
> RTNETLINK answers: No such process
>

So at least we have the routes in the FIB.  It looks like this just 
might be a display issue.

> This is on a machine running 4.1.3, but I have seen it on earlier
> versions in the past.
>
> I don't have great reproduction steps here, I've seen this 4-5 times in
> the past few months (on different hardware).  So far, I haven't really
> found any way of fixing it (deleting and readding the route has no
> effect).  I thought at first this might be related to
> e55ffaf457bcc8ec4e9d9f56f955971f834d65b3, but as far as I can tell that
> only relates to /proc/net/route.
>
> Any suggestions on further troubleshooting here?  I'm all out of ideas
> (and since I can't easily reproduce it yet, I can't reboot to a newer
> kernel to see if it goes away)

How many routes do you have on your system?  I'm just wondering if it 
might be possible that the route could be at a boundary for the dump 
call and if it might be possibly losing the data there.  Although I 
would expect

Also have you tried double checking to verify that grep isn't somehow 
missing the line?

- Alex

Re: Missing IPv4 routes

[Brian Rak]

On 10/23/2015 6:32 PM, Alexander Duyck wrote:
> On 10/23/2015 02:34 PM, Brian Rak wrote:
>> I've got a weird situation here.  I have a route that the kernel knows
>> about, but won't display via the general RTM_GETROUTE call, but will
>> display if I query for that particular route:
>>
>> # ip -4 route show | grep 108.61.171.x
>
> The use of 'x' here is going to make things confusing.  I assume you 
> are using a value of 0 here, or is this a route to a specific IP 
> address that you have.  If not you should be using a 0 for all bits 
> that would be outside of your subnet mask.
>
This is a route to a particular IP address:

# ip route show | grep  108.61.171.247
# ip route get  108.61.171.247
108.61.171.247 dev SRVID630287
     cache

>> # ip route get 108.61.171.x
>> 108.61.171.x dev MYIF
>>      cache
>
> The 'x' being the actual value here should work as this will perform a 
> lookup as I recall.
>
>> # cat /proc/net/route | grep 108.61.171.x
>
> The IPs are in network order and as just hex so this won't work.
>
>> # cat /proc/net/route  | grep -i 6c3dac
>
> The byte ordering you are using is backwards here from what I can 
> tell.  So it should be ac3d6c you are checking for, not the other way 
> around.  So for example if I was using 192.168.1.x I would want to 
> look for 01A8C0.
Oops.  This also doesn't show the route, which it should:

# cat /proc/net/route  | grep SRVID630287
#

>
>> # ip route add 108.61.171.x dev MYIF
>> RTNETLINK answers: File exists
>> # ip route del 108.61.171.x  <---- it deletes successfully once
>> # ip route del 108.61.171.x
>> RTNETLINK answers: No such process
>>
>
> So at least we have the routes in the FIB.  It looks like this just 
> might be a display issue.
>
>> This is on a machine running 4.1.3, but I have seen it on earlier
>> versions in the past.
>>
>> I don't have great reproduction steps here, I've seen this 4-5 times in
>> the past few months (on different hardware).  So far, I haven't really
>> found any way of fixing it (deleting and readding the route has no
>> effect).  I thought at first this might be related to
>> e55ffaf457bcc8ec4e9d9f56f955971f834d65b3, but as far as I can tell that
>> only relates to /proc/net/route.
>>
>> Any suggestions on further troubleshooting here?  I'm all out of ideas
>> (and since I can't easily reproduce it yet, I can't reboot to a newer
>> kernel to see if it goes away)
>
> How many routes do you have on your system?  I'm just wondering if it 
> might be possible that the route could be at a boundary for the dump 
> call and if it might be possibly losing the data there. Although I 
> would expect
ip -4 route show | wc -l shows 67
>
> Also have you tried double checking to verify that grep isn't somehow 
> missing the line?
Yes, so we noticed this issue because BIRD stopped picking up the 
route.  BIRD's trying to grab these via netlink: 
https://github.com/BIRD/bird/blob/master/sysdep/linux/netlink.c#L1045 , 
so I don't believe this is just an issue with grep missing the route.  I 
also wrote a simple  python script with pyroute2, which also missed the 
route.

I was doing some testing to see if I could add routes for nearby IPs, 
and ended up somehow correcting the issue:

# ip route show | grep SRVID630287
# ip route add 108.61.171.200/32 dev SRVID630287
# ip route show | grep SRVID630287
108.61.171.200 dev SRVID630287  scope link
108.61.171.247 dev SRVID630287  scope link
# ip route del 108.61.171.200/32 dev SRVID630287
# ip route show | grep SRVID630287
108.61.171.247 dev SRVID630287  scope link

Does that make any sense?

Re: Missing IPv4 routes

[Alexander Duyck]

On 10/24/2015 06:32 AM, Brian Rak wrote:
>
>
> On 10/23/2015 6:32 PM, Alexander Duyck wrote:
>> On 10/23/2015 02:34 PM, Brian Rak wrote:
>>> I've got a weird situation here.  I have a route that the kernel knows
>>> about, but won't display via the general RTM_GETROUTE call, but will
>>> display if I query for that particular route:
>>>
>>> # ip -4 route show | grep 108.61.171.x
>>
>> The use of 'x' here is going to make things confusing.  I assume you
>> are using a value of 0 here, or is this a route to a specific IP
>> address that you have.  If not you should be using a 0 for all bits
>> that would be outside of your subnet mask.
>>
> This is a route to a particular IP address:
>
> # ip route show | grep  108.61.171.247
> # ip route get  108.61.171.247
> 108.61.171.247 dev SRVID630287
>      cache

Okay, makes sense.

>>> # ip route get 108.61.171.x
>>> 108.61.171.x dev MYIF
>>>      cache
>>
>> The 'x' being the actual value here should work as this will perform a
>> lookup as I recall.
>>
>>> # cat /proc/net/route | grep 108.61.171.x
>>
>> The IPs are in network order and as just hex so this won't work.
>>
>>> # cat /proc/net/route  | grep -i 6c3dac
>>
>> The byte ordering you are using is backwards here from what I can
>> tell.  So it should be ac3d6c you are checking for, not the other way
>> around.  So for example if I was using 192.168.1.x I would want to
>> look for 01A8C0.
> Oops.  This also doesn't show the route, which it should:
>
> # cat /proc/net/route  | grep SRVID630287
> #
>

So does this device have no routes on it then?  I'm just wanting to 
confirm the behaviour you are seeing since my concern was mostly about a 
bug I had introduced where we were losing one route if a dump was broken 
up over multiple pages.  It seems like that isn't the case.

>>
>>> # ip route add 108.61.171.x dev MYIF
>>> RTNETLINK answers: File exists
>>> # ip route del 108.61.171.x  <---- it deletes successfully once
>>> # ip route del 108.61.171.x
>>> RTNETLINK answers: No such process
>>>
>>
>> So at least we have the routes in the FIB.  It looks like this just
>> might be a display issue.
>>
>>> This is on a machine running 4.1.3, but I have seen it on earlier
>>> versions in the past.
>>>
>>> I don't have great reproduction steps here, I've seen this 4-5 times in
>>> the past few months (on different hardware).  So far, I haven't really
>>> found any way of fixing it (deleting and readding the route has no
>>> effect).  I thought at first this might be related to
>>> e55ffaf457bcc8ec4e9d9f56f955971f834d65b3, but as far as I can tell that
>>> only relates to /proc/net/route.
>>>
>>> Any suggestions on further troubleshooting here?  I'm all out of ideas
>>> (and since I can't easily reproduce it yet, I can't reboot to a newer
>>> kernel to see if it goes away)
>>
>> How many routes do you have on your system?  I'm just wondering if it
>> might be possible that the route could be at a boundary for the dump
>> call and if it might be possibly losing the data there. Although I
>> would expect
> ip -4 route show | wc -l shows 67
>>
>> Also have you tried double checking to verify that grep isn't somehow
>> missing the line?
> Yes, so we noticed this issue because BIRD stopped picking up the
> route.  BIRD's trying to grab these via netlink:
> https://github.com/BIRD/bird/blob/master/sysdep/linux/netlink.c#L1045 ,
> so I don't believe this is just an issue with grep missing the route.  I
> also wrote a simple  python script with pyroute2, which also missed the
> route.
>
> I was doing some testing to see if I could add routes for nearby IPs,
> and ended up somehow correcting the issue:
>
> # ip route show | grep SRVID630287
> # ip route add 108.61.171.200/32 dev SRVID630287
> # ip route show | grep SRVID630287
> 108.61.171.200 dev SRVID630287  scope link
> 108.61.171.247 dev SRVID630287  scope link
> # ip route del 108.61.171.200/32 dev SRVID630287
> # ip route show | grep SRVID630287
> 108.61.171.247 dev SRVID630287  scope link
>
> Does that make any sense?

It might if there is a hole in what is being displayed.  One thing you 
might try doing is to generate two dumps, one with your additional route 
and one without and then try doing a diff between the two.  Then you 
might look at adding a few more routes to see if that forces the missing 
route to appear but perhaps causes another route to disappear from the dump.

With that test we should be able to identify the behaviour since it 
sounds like an issue where the route is there in memory, but for 
whatever reason it isn't being displayed.  If we can identify a hole 
that these routes are falling into we might be able to determine what is 
causing the issue.

- Alex

Re: Missing IPv4 routes

[Brian Rak]

On 10/26/2015 11:28 AM, Alexander Duyck wrote:
> On 10/24/2015 06:32 AM, Brian Rak wrote:
>>
>>
>> On 10/23/2015 6:32 PM, Alexander Duyck wrote:
>>> On 10/23/2015 02:34 PM, Brian Rak wrote:
>>>> I've got a weird situation here.  I have a route that the kernel knows
>>>> about, but won't display via the general RTM_GETROUTE call, but will
>>>> display if I query for that particular route:
>>>>
>>>> # ip -4 route show | grep 108.61.171.x
>>>
>>> The use of 'x' here is going to make things confusing.  I assume you
>>> are using a value of 0 here, or is this a route to a specific IP
>>> address that you have.  If not you should be using a 0 for all bits
>>> that would be outside of your subnet mask.
>>>
>> This is a route to a particular IP address:
>>
>> # ip route show | grep  108.61.171.247
>> # ip route get  108.61.171.247
>> 108.61.171.247 dev SRVID630287
>>      cache
>
> Okay, makes sense.
>
>>>> # ip route get 108.61.171.x
>>>> 108.61.171.x dev MYIF
>>>>      cache
>>>
>>> The 'x' being the actual value here should work as this will perform a
>>> lookup as I recall.
>>>
>>>> # cat /proc/net/route | grep 108.61.171.x
>>>
>>> The IPs are in network order and as just hex so this won't work.
>>>
>>>> # cat /proc/net/route  | grep -i 6c3dac
>>>
>>> The byte ordering you are using is backwards here from what I can
>>> tell.  So it should be ac3d6c you are checking for, not the other way
>>> around.  So for example if I was using 192.168.1.x I would want to
>>> look for 01A8C0.
>> Oops.  This also doesn't show the route, which it should:
>>
>> # cat /proc/net/route  | grep SRVID630287
>> #
>>
>
> So does this device have no routes on it then?  I'm just wanting to 
> confirm the behaviour you are seeing since my concern was mostly about 
> a bug I had introduced where we were losing one route if a dump was 
> broken up over multiple pages.  It seems like that isn't the case.
These devices only usually have a single IPv4 route, so seeing no other 
routes there is what I'd expect.

>
>>>
>>>> # ip route add 108.61.171.x dev MYIF
>>>> RTNETLINK answers: File exists
>>>> # ip route del 108.61.171.x  <---- it deletes successfully once
>>>> # ip route del 108.61.171.x
>>>> RTNETLINK answers: No such process
>>>>
>>>
>>> So at least we have the routes in the FIB.  It looks like this just
>>> might be a display issue.
>>>
>>>> This is on a machine running 4.1.3, but I have seen it on earlier
>>>> versions in the past.
>>>>
>>>> I don't have great reproduction steps here, I've seen this 4-5 
>>>> times in
>>>> the past few months (on different hardware).  So far, I haven't really
>>>> found any way of fixing it (deleting and readding the route has no
>>>> effect).  I thought at first this might be related to
>>>> e55ffaf457bcc8ec4e9d9f56f955971f834d65b3, but as far as I can tell 
>>>> that
>>>> only relates to /proc/net/route.
>>>>
>>>> Any suggestions on further troubleshooting here?  I'm all out of ideas
>>>> (and since I can't easily reproduce it yet, I can't reboot to a newer
>>>> kernel to see if it goes away)
>>>
>>> How many routes do you have on your system?  I'm just wondering if it
>>> might be possible that the route could be at a boundary for the dump
>>> call and if it might be possibly losing the data there. Although I
>>> would expect
>> ip -4 route show | wc -l shows 67
>>>
>>> Also have you tried double checking to verify that grep isn't somehow
>>> missing the line?
>> Yes, so we noticed this issue because BIRD stopped picking up the
>> route.  BIRD's trying to grab these via netlink:
>> https://github.com/BIRD/bird/blob/master/sysdep/linux/netlink.c#L1045 ,
>> so I don't believe this is just an issue with grep missing the route.  I
>> also wrote a simple  python script with pyroute2, which also missed the
>> route.
>>
>> I was doing some testing to see if I could add routes for nearby IPs,
>> and ended up somehow correcting the issue:
>>
>> # ip route show | grep SRVID630287
>> # ip route add 108.61.171.200/32 dev SRVID630287
>> # ip route show | grep SRVID630287
>> 108.61.171.200 dev SRVID630287  scope link
>> 108.61.171.247 dev SRVID630287  scope link
>> # ip route del 108.61.171.200/32 dev SRVID630287
>> # ip route show | grep SRVID630287
>> 108.61.171.247 dev SRVID630287  scope link
>>
>> Does that make any sense?
>
> It might if there is a hole in what is being displayed.  One thing you 
> might try doing is to generate two dumps, one with your additional 
> route and one without and then try doing a diff between the two.  Then 
> you might look at adding a few more routes to see if that forces the 
> missing route to appear but perhaps causes another route to disappear 
> from the dump.
>
> With that test we should be able to identify the behaviour since it 
> sounds like an issue where the route is there in memory, but for 
> whatever reason it isn't being displayed.  If we can identify a hole 
> that these routes are falling into we might be able to determine what 
> is causing the issue.

I had added some other routes randomly here (1.1.1.1/32, 
200.200.200.200/32, 108.61.172.249/32).  I didn't see this route 
reappear until I added one in the same /24, but I wasn't checking for 
other routes going missing.

I'm not entirely sure how, but adding that one extra route 
(108.61.171.200/32 dev SRVID630287) appears to have permanently fixed 
the issue.  Even after removing that extra route, the original route 
still appears.

I've been able to come up with some reproduction steps here, and 
verified that this still happens on 4.2.4:

# ip route show
default via 45.63.12.1 dev eth0  proto static
45.63.12.0/23 dev eth0  proto kernel  scope link  src 45.63.13.197
169.254.0.0/16 dev eth0  scope link
169.254.0.0/16 dev eth0  scope link  metric 1002
# ip link add veth0 type veth peer name veth1
# ip link set veth0 up
# ip link set veth1 up
#
# ip route add 108.61.171.119/32 dev veth0  scope link
# ip route add 108.61.171.141/32 dev veth1  scope link
# ip route add 108.61.171.223/32 dev veth1  scope link
# ip route add 108.61.171.250/32 dev veth1  scope link
# ip route add 108.61.171.247/32 dev veth1  scope link
# ip route show
default via 45.63.12.1 dev eth0  proto static
45.63.12.0/23 dev eth0  proto kernel  scope link  src 45.63.13.197
108.61.171.119 dev veth0  scope link
108.61.171.141 dev veth1  scope link
108.61.171.223 dev veth1  scope link
<--- ROUTES MISSING!
169.254.0.0/16 dev eth0  scope link
169.254.0.0/16 dev eth0  scope link  metric 1002
# ip route get 108.61.171.250/32
108.61.171.250 dev veth1  src 45.63.13.197
     cache
# ip route get 108.61.171.247/32
108.61.171.247 dev veth1  src 45.63.13.197
     cache
# ip route del 108.61.171.250/32
# ip route show
default via 45.63.12.1 dev eth0  proto static
45.63.12.0/23 dev eth0  proto kernel  scope link  src 45.63.13.197
108.61.171.119 dev veth0  scope link
108.61.171.141 dev veth1  scope link
108.61.171.223 dev veth1  scope link
108.61.171.247 dev veth1  scope link <----- comes back
169.254.0.0/16 dev eth0  scope link
169.254.0.0/16 dev eth0  scope link  metric 1002
# ip route add 108.61.171.250/32 dev veth1
# ip route show
default via 45.63.12.1 dev eth0  proto static
45.63.12.0/23 dev eth0  proto kernel  scope link  src 45.63.13.197
108.61.171.119 dev veth0  scope link
108.61.171.141 dev veth1  scope link
108.61.171.223 dev veth1  scope link
<--- gone again
169.254.0.0/16 dev eth0  scope link
169.254.0.0/16 dev eth0  scope link  metric 1002

Re: Missing IPv4 routes

[Brian Rak]

(Existing email got kinda messy, starting over again):

So, I'm having an issue with the kernel where if I add a bunch of 
routes, I see some of them go "missing".  They don't show up in the 'ip 
-4 route' list, but they do show up if I do 'ip -4 route get X'.

I managed to come up with a simple set of reproduction commands:

ip link add veth0 type veth peer name veth1
ip link set veth0 up
ip link set veth1 up

ip route add 108.61.171.119/32 dev veth0  scope link
ip route add 108.61.171.141/32 dev veth1  scope link
ip route add 108.61.171.223/32 dev veth1  scope link
ip route add 108.61.171.250/32 dev veth1  scope link
ip route add 108.61.171.247/32 dev veth1  scope link

ip route show

In the route show, you'll see 108.61.171.250/32 and 108.61.171.247/32 
missing completely.

I did a lot of bisecting, and traced it down to this commit:

commit 8be33e955cb959dabc1a6eef0b7356fe8cf73fa6
Author: Alexander Duyck <alexander.h.duyck@redhat.com>
Date:   Wed Mar 4 14:59:19 2015 -0800

     fib_trie: Fib walk rcu should take a tnode and key instead of a 
trie and a leaf

The commit immediately prior to this one 
(7289e6ddb633aaee6ccea2bd2e410654c47b29a6) works fine.

I tried the off-by-one fix from 
e55ffaf457bcc8ec4e9d9f56f955971f834d65b3, however this doesn't appear to 
help at all.   This code is a little above my head, so I don't really 
understand what exactly is broken here.

Re: Missing IPv4 routes

[Alexander Duyck]

On 10/27/2015 01:01 PM, Brian Rak wrote:
> (Existing email got kinda messy, starting over again):
>
> So, I'm having an issue with the kernel where if I add a bunch of 
> routes, I see some of them go "missing".  They don't show up in the 
> 'ip -4 route' list, but they do show up if I do 'ip -4 route get X'.
>
> I managed to come up with a simple set of reproduction commands:
>
> ip link add veth0 type veth peer name veth1
> ip link set veth0 up
> ip link set veth1 up
>
> ip route add 108.61.171.119/32 dev veth0  scope link
> ip route add 108.61.171.141/32 dev veth1  scope link
> ip route add 108.61.171.223/32 dev veth1  scope link
> ip route add 108.61.171.250/32 dev veth1  scope link
> ip route add 108.61.171.247/32 dev veth1  scope link
>
> ip route show
>
> In the route show, you'll see 108.61.171.250/32 and 108.61.171.247/32 
> missing completely.
>
> I did a lot of bisecting, and traced it down to this commit:
>
> commit 8be33e955cb959dabc1a6eef0b7356fe8cf73fa6
> Author: Alexander Duyck <alexander.h.duyck@redhat.com>
> Date:   Wed Mar 4 14:59:19 2015 -0800
>
>     fib_trie: Fib walk rcu should take a tnode and key instead of a 
> trie and a leaf
>
> The commit immediately prior to this one 
> (7289e6ddb633aaee6ccea2bd2e410654c47b29a6) works fine.
>
> I tried the off-by-one fix from 
> e55ffaf457bcc8ec4e9d9f56f955971f834d65b3, however this doesn't appear 
> to help at all.   This code is a little above my head, so I don't 
> really understand what exactly is broken here.

I'll take a look at it and see if I can come up with a fix by this 
afternoon.

Thanks.

- Alex