Re: VRF Issue Since kernel 5

[Alexis Bauvin <abauvin@online.net>]

Hi,

There has been some changes regarding VRF isolation in Linux 5 IIRC, namely proper
isolation of the default VRF.

Some things you may try:

- looking at the l3mdev_accept sysctls (e.g. `net.ipv4.tcp_l3mdev_accept`)
- querying stuff from the management vrf through `ip vrf exec vrf-mgmt <stuff>`
  e.g. `ip vrf exec vrf-mgmt curl kernel.org`
       `ip vrf exec vrf-mgmt dig @1.1.1.1 kernel.org`
- reversing your logic: default VRF is your management one, the other one is for your
  other boxes

Also, your `unreachable default metric 4278198272` route looks odd to me.

What are your routing rules? (`ip rule`)

Alexis

> Le 9 sept. 2019 à 09:46, Gowen <gowen@potatocomputing.co.uk> a écrit :
> 
> Hi there,
> 
> Dave A said this was the mailer to send this to:
> 
> 
> I’ve been using my management interface in a VRF for several months now and it’s worked perfectly – I’ve been able to update/upgrade the packages just fine and iptables works excellently with it – exactly as I needed.
> 
> 
> Since Kernel 5 though I am no longer able to update – but the issue is quite a curious one as some traffic appears to be fine (DNS lookups use VRF correctly) but others don’t (updating/upgrading the packages)
> 
> 
> I have on this device 2 interfaces:
> Eth0 for management – inbound SSH, DNS, updates/upgrades
> Eth1 for managing other boxes (ansible using SSH)
> 
> 
> Link and addr info shown below:
> 
> 
> Admin@NETM06:~$ ip link show
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master mgmt-vrf state UP mode DEFAULT group default qlen 1000
>     link/ether 00:22:48:07:cc:ad brd ff:ff:ff:ff:ff:ff
> 3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
>     link/ether 00:22:48:07:c9:6c brd ff:ff:ff:ff:ff:ff
> 4: mgmt-vrf: <NOARP,MASTER,UP,LOWER_UP> mtu 65536 qdisc noqueue state UP mode DEFAULT group default qlen 1000
>     link/ether 8a:f6:26:65:02:5a brd ff:ff:ff:ff:ff:ff
> 
> 
> Admin@NETM06:~$ ip addr
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>     inet 127.0.0.1/8 scope host lo
>        valid_lft forever preferred_lft forever
>     inet6 ::1/128 scope host
>        valid_lft forever preferred_lft forever
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master mgmt-vrf state UP group default qlen 1000
>     link/ether 00:22:48:07:cc:ad brd ff:ff:ff:ff:ff:ff
>     inet 10.24.12.10/24 brd 10.24.12.255 scope global eth0
>        valid_lft forever preferred_lft forever
>     inet6 fe80::222:48ff:fe07:ccad/64 scope link
>        valid_lft forever preferred_lft forever
> 3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
>     link/ether 00:22:48:07:c9:6c brd ff:ff:ff:ff:ff:ff
>     inet 10.24.12.9/24 brd 10.24.12.255 scope global eth1
>        valid_lft forever preferred_lft forever
>     inet6 fe80::222:48ff:fe07:c96c/64 scope link
>        valid_lft forever preferred_lft forever
> 4: mgmt-vrf: <NOARP,MASTER,UP,LOWER_UP> mtu 65536 qdisc noqueue state UP group default qlen 1000
>     link/ether 8a:f6:26:65:02:5a brd ff:ff:ff:ff:ff:ff
> 
> 
> 
> the production traffic is all in the 10.0.0.0/8 network (eth1 global VRF) except for a few subnets (DNS) which are routed out eth0 (mgmt-vrf)
> 
> 
> Admin@NETM06:~$ ip route show
> default via 10.24.12.1 dev eth0
> 10.0.0.0/8 via 10.24.12.1 dev eth1
> 10.24.12.0/24 dev eth1 proto kernel scope link src 10.24.12.9
> 10.24.65.0/24 via 10.24.12.1 dev eth0
> 10.25.65.0/24 via 10.24.12.1 dev eth0
> 10.26.0.0/21 via 10.24.12.1 dev eth0
> 10.26.64.0/21 via 10.24.12.1 dev eth0
> 
> 
> Admin@NETM06:~$ ip route show vrf mgmt-vrf
> default via 10.24.12.1 dev eth0
> unreachable default metric 4278198272
> 10.24.12.0/24 dev eth0 proto kernel scope link src 10.24.12.10
> 10.24.65.0/24 via 10.24.12.1 dev eth0
> 10.25.65.0/24 via 10.24.12.1 dev eth0
> 10.26.0.0/21 via 10.24.12.1 dev eth0
> 10.26.64.0/21 via 10.24.12.1 dev eth0
> 
> 
> 
> The strange activity occurs when I enter the command “sudo apt update” as I can resolve the DNS request (10.24.65.203 or 10.24.64.203, verified with tcpdump) out eth0 but for the actual update traffic there is no activity:
> 
> 
> sudo tcpdump -i eth0 '(host 10.24.65.203 or host 10.25.65.203) and port 53' -n
> <OUTPUT OMITTED FOR BREVITY>
> 10:06:05.268735 IP 10.24.12.10.39963 > 10.24.65.203.53: 48798+ [1au] A? security.ubuntu.com. (48)
> <OUTPUT OMITTED FOR BREVITY>
> 10:06:05.284403 IP 10.24.65.203.53 > 10.24.12.10.39963: 48798 13/0/1 A 91.189.91.23, A 91.189.88.24, A 91.189.91.26, A 91.189.88.162, A 91.189.88.149, A 91.189.91.24, A 91.189.88.173, A 91.189.88.177, A 91.189.88.31, A 91.189.91.14, A 91.189.88.176, A 91.189.88.175, A 91.189.88.174 (256)
> 
> 
> 
> You can see that the update traffic is returned but is not accepted by the stack and a RST is sent
> 
> 
> Admin@NETM06:~$ sudo tcpdump -i eth0 '(not host 168.63.129.16 and port 80)' -n
> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
> listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
> 10:17:12.690658 IP 10.24.12.10.40216 > 91.189.88.175.80: Flags [S], seq 2279624826, win 64240, options [mss 1460,sackOK,TS val 2029365856 ecr 0,nop,wscale 7], length 0
> 10:17:12.691929 IP 10.24.12.10.52362 > 91.189.95.83.80: Flags [S], seq 1465797256, win 64240, options [mss 1460,sackOK,TS val 3833463674 ecr 0,nop,wscale 7], length 0
> 10:17:12.696270 IP 91.189.88.175.80 > 10.24.12.10.40216: Flags [S.], seq 968450722, ack 2279624827, win 28960, options [mss 1418,sackOK,TS val 81957103 ecr 2029365856,nop,wscale 7], length 0                                                                                                                            
> 10:17:12.696301 IP 10.24.12.10.40216 > 91.189.88.175.80: Flags [R], seq 2279624827, win 0, length 0
> 10:17:12.697884 IP 91.189.95.83.80 > 10.24.12.10.52362: Flags [S.], seq 4148330738, ack 1465797257, win 28960, options [mss 1418,sackOK,TS val 2257624414 ecr 3833463674,nop,wscale 8], length 0                                                                                                                         
> 10:17:12.697909 IP 10.24.12.10.52362 > 91.189.95.83.80: Flags [R], seq 1465797257, win 0, length 0
> 
> 
> 
> 
> I can emulate the DNS lookup using netcat in the vrf:
> 
> 
> sudo ip vrf exec mgmt-vrf nc -u 10.24.65.203 53
> 
> 
> then interactively enter the binary for a www.google.co.uk request:
> 
> 
> 0035624be394010000010000000000010377777706676f6f676c6502636f02756b00000100010000290200000000000000
> 
> 
> This returns as expected:
> 
> 
> 00624be394010000010000000000010377777706676f6f676c6502636f02756b00000100010000290200000000000000
> 
> 
> I can run:
> 
> 
> Admin@NETM06:~$ host www.google.co.uk
> www.google.co.uk has address 172.217.169.3
> www.google.co.uk has IPv6 address 2a00:1450:4009:80d::2003
> 
> 
> but I get a timeout for:
> 
> 
> sudo ip vrf  exec mgmt-vrf host www.google.co.uk
> ;; connection timed out; no servers could be reached
> 
> 
> 
> However I can take a repo address and vrf exec to it on port 80:
> 
> 
> Admin@NETM06:~$ sudo ip vrf  exec mgmt-vrf nc 91.189.91.23 80
> hello
> HTTP/1.1 400 Bad Request
> <OUTPUT OMITTED>
> 
> My iptables rule:
> 
> 
> sudo iptables -Z
> Admin@NETM06:~$ sudo iptables -L -v
> Chain INPUT (policy DROP 16 packets, 3592 bytes)
> pkts bytes target     prot opt in     out     source               destination
>    44  2360 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp spt:http ctstate RELATED,ESTABLISHED
>    83 10243 ACCEPT     udp  --  any    any     anywhere             anywhere             udp spt:domain ctstate RELATED,ESTABLISHED
> 
> 
> 
> I cannot find out why the update isn’t working. Any help greatly appreciated
> 
> 
> Kind Regards,
> 
> 
> Gareth