December 2021 - Bird-users

Re: BIRD trying to reinsert existing kernel routes, netlink issue?
by Zhaofeng Li 18 Feb '22

18 Feb '22

I know this was an old thread, but would really appreciate if anyone is interested in digging in deeper. I can confirm the exact same behavior happens to me on NixOS with the 5.4.69 kernel but not on 4.19.149. BIRD 2.0.7 on 5.4.69 would incessantly attempt to insert the same routes, rendering birdc unusable as it was presumably taking up so much time in the main loop (it was receiving an IPv4 full table over iBGP as well). While it was doing that, it stopped announcing the prefixes of stub interfaces to OSPF neighbors. Thanks, Zhaofeng Li On Sun, Aug 2, 2020, at 17:36 PM, Sasha Romijn wrote: > Hello, > I’m running into a rather complex issue where BIRD tries to reinsert routes into the kernel routing table that are already in there. I’m at the point of suspecting a netlink bug in the 5.x linux kernel. However, I may be entirely off, and would like to hear what people with more BIRD and/or netlink expertise think about it. > My setup is bird 2.0.7 on Ubuntu 20.04. I’ve been able to reproduce this with the default 5.4.0-42-generic kernel as well as the ubuntu mainline 5.7.0-050700-generic kernel. This bird instance has an IBGP peering with another bird 2.0.7 instance, which sends an IPv4 full table. The IBGP peering is set up over a GRE tunnel. There is no other routing software running. I am seeing this issue on another server too, ubuntu 20.04 with 5.4.0-42-generic. A third one with ubuntu 18.04 and a 4.15.0-20-generic kernel, is fine.

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Route Flapping and Bird - RFD and MRAI
by Douglas Fischer 16 Feb '22

16 Feb '22

Hello all. Last weeks I'm noticing the increase the increase of BGP messages on some routers that I have access to. Specially those connected to IXPs with a considerable number of participants. I Checked and the BGP process has increased a bit the use of CPU Also. So, I suspect that Route-Servers are receiving and forwarding Route Flaps from one or more participants... I know that the right place to fix that would be on the source of those flaps... But... Considering IXPs with one ou two thousand participants, there will always be someone flapping some routes. Bird is widely used as the BGP engine on IXP route-servers. And exactly because of that I came here to ask about Route Flap avoidance mechanisms on Bird. The discussion of methods to avoid Route Flapping in BGP is very controversial. - RFD - Route Flapping Dampening comes and goes. - MRAI is not a consensus, but there is a lot of effort on that, including som magic algorithms define some variable interval according to conditions. - I even saw some ultra-rigorous ideas like rate limiting the BGP messages... Before I come here to bore you with this, I searched a bit on mail list and documentation of Bird and I found the links bellow related to that: There is any work running to deal with that route-flapping question? https://bird.network.cz/ - 7.1 Future work <https://bird.network.cz/?get_doc&v=20&f=bird-7.html> Question about BGP advertisement-interval in BIRD <http://trubka.network.cz/pipermail/bird-users/2020-August/014786.html> [BGP] MRAI connection-based implementation review <http://trubka.network.cz/pipermail/bird-users/2020-April/014433.html> Route Flap Dampening <http://trubka.network.cz/pipermail/bird-users/2019-July/013589.html> [BGP] bird and RFD <http://trubka.network.cz/pipermail/bird-users/2020-May/014612.html> Thank you all! -- Douglas Fernando Fischer Engº de Controle e Automação

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BIRD multithreaded progress
by Ross Tajvar 10 Feb '22

10 Feb '22

Hi BIRD team, I have been periodically checking the cz.nic blog for more posts in the "BIRD multithreading" saga, but the latest one was about 5.5 months ago ( https://en.blog.nic.cz/2021/06/14/bird-journey-to-threads-chapter-2-asynchr…) Has any more progress been made on this? I understand the team is busy and I'm not trying to push, but I enjoy reading these posts and keeping up with the work being done. Best, Ross

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BGP strict bind socket error
by Ben Tremblay 09 Jan '22

09 Jan '22

Hi all, I have encountered a problem with how BIRD opens the listening socket for strict bind BGP. In particular, BIRD sometimes tries to open the listening socket for the protocol when the configured local IP is not yet present on the interface. It seems that BIRD will try to bind the BGP socket to the configured IP if any address exists on the protocol interface that can be used to reach the neighbor. Let me give an example to clarify. I have a minimal reproducible example with the following BGP configuration: router id 192.168.0.1; protocol device { scan time 10; } protocol bgp bgp_01 { ipv4 { import all; export all; }; debug all; local 192.168.0.1 port 179 as 1; neighbor 192.168.0.2 port 179 as 1; interface "host1"; direct; strict bind yes; } Given this configuration, I can reproduce the problem behaviour by starting the protocol with no addressing on the host1 interface and then adding an address which includes the neighbor IP in its subnet, e.g. 192.168.0.3/24. Once this address/route is added, BIRD logs the following: Jan 07 12:09:31 router03 bird[57497]: bgp_01: Neighbor ready Jan 07 12:09:31 router03 bird[57497]: bgp_01: Socket error: bind: Cannot assign requested address Jan 07 12:09:31 router03 bird[57497]: bgp_01: Cannot open listening socket And the protocol enters an error state: BIRD 2.0.6 ready. Name Proto Table State Since Info device1 Device --- up 11:55:51.049 bgp_01 BGP --- down 12:09:31.264 Error: No listening socket The reason this error is so problematic for me is that the protocol cannot recover from this state without administrative intervention (e.g. configuring bird or restarting the protocol). So, I have two questions: 1. Is this correct behaviour? 2. Can I configure BIRD so that my protocol is able to recover after suffering a socket error like this? I should also mention I can actually observe this socket error occur when adding the 'correct' address to the protocol interface, but only in the context of a larger application and only some of the time. Thanks, Ben

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[BIRD 2.0.x] Netlink: ignore dead routes
by Vincent Bernat 09 Jan '22

09 Jan '22

With net.ipv4.conf.XXX.ignore_routes_with_linkdown sysctl, a user can ensure the kernel does not use a route whose target interface is down. The route is marked with a "dead"/RTNH_F_DEAD flag. Currently, BIRD still uses and distributes this route. This patch just ignores such a route. This patch could be backported to 1.6.x. Signed-off-by: Vincent Bernat <vincent(a)bernat.ch> --- sysdep/linux/netlink.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/sysdep/linux/netlink.c b/sysdep/linux/netlink.c index f85bcf35685b..c28126510e6e 100644 --- a/sysdep/linux/netlink.c +++ b/sysdep/linux/netlink.c @@ -1690,6 +1690,9 @@ nl_parse_route(struct nl_parse_state *s, struct nlmsghdr *h) if (i->rtm_flags & RTNH_F_ONLINK) ra->nh.flags |= RNF_ONLINK; + if (i->rtm_flags & RTNH_F_DEAD) + return; + neighbor *nbr; nbr = neigh_find(&p->p, ra->nh.gw, ra->nh.iface, (ra->nh.flags & RNF_ONLINK) ? NEF_ONLINK : 0); -- 2.28.0

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Re: BIRD 2.0 on FreeBSD, multihop with multiple fibs
by Dominic Blais 01 Jan '22

01 Jan '22

Hi, I've had my load of issues with bird 2 on FreeBSD. I used BSDRP like 3 years ago and after an update I started having big issues related to bird. I think BSDRP released version 1.98 with a fix for that.. don't know if it's ok in 1.99. https://sourceforge.net/projects/bsdrp/files/BSD_Router_Project/1.98/ "bird2: Fix multi-FIB usage by reverting bird commit 318acb0f6cb77a32aad5d7f79e06f3c5065ac702" Maybe it's not related but just in case... please tell me if it worked! In reponse to: Hi everyone, I hope this is not too specific... I'm running into a bit of a pickle here. This is FreeBSD 12.2 with multi-fib enabled; BIRD exporting all its received routes to fib 1, basic kernel routing in fib 0. (The service on the box is in fib 1, of course). I need to configure a multihop session where the BGP partner is not on the same interface as the box's default, but on a pni, which is behind a VLAN-tagged subinterface (i.e., bge0.300) down on a switch somewhere. Also, I can only BGP connect to the partner via the PNI. The interface has no fib tags, so it "exists" in both fibs. Let's say we are bge0.300 5.6.7.7. The other side of the PNI is at 5.6.7.8. Our BGP partner is at 1.2.3.4, reachable through 5.6.7.8. protocol static { ipv4; route 1.2.3.4/32 via 5.6.7.8; } Now, netstat tells me that 1.2.3.4/32 shows up in fib 1, but not in fib 0. BIRD only puts it in fib 1. In this setup, BIRD does not connect to 1.2.3.4 unless I manually add that host route to fib 0. Adding a % 'bge0.300' to the static route line doesn't change a thing, route still only appears in fib 1. Two questions: - why does BIRD put the route in fib 1 when no fib is specified, and the interface is not bound to a fib? - Is there a canonical way of solving this? I have the fib 0 static route configured in the system setup now, which makes it work. It would be nicer to have it thrown in there by BIRD, so the config is self-contained. Any guidance would be highly appreciated. Elmar.

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[PATCH] Filter: picking community elements and finding min/max element
by Alexander Zubkov 28 Dec '21

28 Dec '21

Hi everyone! I made a couple of patches to do some interesting stuff with communities. The first patch allows to pick a component from a standard or a large community: (10, 20, 30) @ 2 --> 20 And the second patch allows to search for minimum or maximum element in a community list. This combined allows to do some cool stuff with communities like this: bgp_local_pref = filter(bgp_large_community, [(<as>, <localpref_val>, *)]).min @ 3 This will find us the minimum from our "localpref" communities and get that number as integer, ready to assign it where we need. Now we use a series of if's to check all the possible variants and that is not very convenient. I think this features will greatly boost the possibilities of working with communities in bird.

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Possibility to treat /32 and /128 non-gateway routes as onlink on BSD?
by Stefan Haller 27 Dec '21

27 Dec '21

Hi everyone, In a recent change in the FreeBSD Wireguard kernel module the POINTTOPOINT interface flag is dropped for wg interfaces[1]. This behaviour will probably not change, because Wireguard is not peer-to-peer or a broadcast domain, but peer-to-multipoint. Hence my previous configuration of setting peer addresses on the interface is not working anymore: ifconfig wg0 inet 192.168.0.10/32 192.168.0.4 The above syntax is for POINTTOPOINT interfaces. In this case 192.168.0.10 is the local address of the interface and 192.168.0.4 is the address of the remote peer. So if one does not want to add a dedicated subnet to every tunnel device, one has to add static host routes similar to these ones: ifconfig wg0 192.168.0.10/32 route add 192.168.0.4 -iface wg0 Note that this actually models the real world better, because Wireguard is not point-to-point but point-to-multipoint. So multiple peers can be done in the following way: ifconfig wg0 192.168.0.10/32 route add 192.168.0.4 -iface wg0 route add 192.168.0.8 -iface wg0 However, this does not work with bird 2.0.8: bird will not recognize the p2p peer addresses as gateways and it will log on kernel table rescan: KRT: Received route 192.168.42.0/24 with strange next-hop 192.168.0.4 KRT: Error sending route 192.168.42.0/24 to kernel: File exists I did have a look why this is happening: bird discards the route, because the gateway does not belong to any of its interface's addresses (the peer address is configured as a static host route and not on the interface). At the same time it forgets that it was bird itself who added the route (because the route is discarded on kernel table rescan, it thinks it is absent in the kernel table but present in bird's internal routing table -> "add" logic triggers) and tries to add the route again (instead of replacing/keeping the route). This explains the cascade of error messages above. While the Linux netlink code allows to handle onlink routes, this functionality is absent in the BSD code path. Unfortunately, on BSD there is no dedicated flag to mark routes as being directly connected onlink routes. On Linux one could add an onlink route like so: ip route add 192.168.0.4 via 192.168.0.4 dev wg0 onlink The command looks quite odd, but it is working. The via clause is necessary in conjunction with onlink. Afterwards a `birdc dump neighbors` verifies that the peer is recognized: 000055db793035c0 192.168.0.4 wg0 wg0 kernel1 000000000000000000000000 scope univ ONLINK (Also the "strange next-hop" message will go away.) I created a patch that emulates the behaviour on FreeBSD. In this patch the onlink setting is heuristically determined by inspecting the RTF_GATEWAY flag (which must be absent) and checking for a /32 or /128 prefix length. I do not see how to handle cases where the destination is a subnet. The patch was tested on FreeBSD 13.0-RELEASE and 14.0-CURRENT. During rescan of the kernel table the above route is now not dropped because the gateway is recognized to be onlink. While in the Linux route the gateway is still set, on FreeBSD it is unset (~RTF_GATEWAY). So I actually use the destination address of the route, because that's the address of the peer. While I tested the functionality on my machines and also checked the output of `birdc dump neighbors`, the patch might be faulty. Please be kind with me and treat it more as a proof of concept. As I am not experienced with bird's code base I do not fully understand how the neighbor cache is working in detail, so the suggested patch might have unexpected side effects. I would appreciate feedback. In case you think the whole idea is not sensible, I would also love to hear suggestions how to get the above setup working. Kind regards, Stefan [1]: https://git.zx2c4.com/wireguard-freebsd/commit/?id=8801509656e955c27ebf4b9b… sysdep/bsd/krt-sock.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/sysdep/bsd/krt-sock.c b/sysdep/bsd/krt-sock.c index ea0cc4d9..4a0f3a7a 100644 --- a/sysdep/bsd/krt-sock.c +++ b/sysdep/bsd/krt-sock.c @@ -547,6 +547,12 @@ krt_read_route(struct ks_msg *msg, struct krt_proto *p, int scan) net->n.addr, a.nh.gw); return; } + } else if ((!ipv6 && pxlen == 32) || (ipv6 && pxlen == 128)) { + /* Treat non gateway /32 and /128 routes as onlink routes and inject this + information into neighbor cache. */ + if (!neigh_find(&p->p, idst, a.nh.iface, NEF_ONLINK)) + log(L_ERR, "KRT: Failed to inject onlink neighbor %I for interface %s", + idst, a.nh.iface->name); } done: -- 2.31.1

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[patch] Add contextual out-of-bound checks in RTR Prefix PDU handler
by Job Snijders 18 Dec '21

18 Dec '21

Hi, A broken RPKI Cache could contextually underflow or overflow the Max Length value in RTR IPv4 / IPv6 Prefix PDUs. Below is a changeset proposal which adds specific out-of-bounds checks and schedules a reconnect for a later moment. This aligns BIRD's behavior with other COTS BGP implementations. RFC 6810 and RFC 8210 specify that the "Max Length" value MUST NOT be less than the Prefix Length element (underflow). On the other side overflow of the Max Length element also is possible, it being an 8-bit unsigned integer allows for values larger than 32 or 128. When a PDU is received where the Max Length field is corrputed, the RTR client (BIRD) should immediately terminate the session, flush all data learned from that cache, and log an error for the operator. If this condition is hit, it seems better to follow the same approach as for RPKI_CS_ERROR_TRANSPORT, because rpki_force_restart_proto() causes an "as fast as possible" reconnect loop between BIRD and the RPKI Cache server, which increases resource consumption on both sides. Kind regards, Job diff --git proto/rpki/packets.c proto/rpki/packets.c index dd11f997..09e20f38 100644 --- proto/rpki/packets.c +++ proto/rpki/packets.c @@ -737,6 +737,22 @@ rpki_handle_prefix_pdu(struct rpki_cache *cache, const struct pdu_header *pdu) net_addr_union addr = {}; rpki_prefix_pdu_2_net_addr(pdu, &addr); + if (type == IPV4_PREFIX) { + if (addr.roa4.max_pxlen > IP4_MAX_PREFIX_LENGTH || addr.roa4.max_pxlen < addr.roa4.pxlen) { + RPKI_WARN(cache->p, "Received a corrupted packet from cache server"); + rpki_send_error_pdu(cache, CORRUPT_DATA, pdu->len, pdu, "Corrupted PDU"); + rpki_cache_change_state(cache, RPKI_CS_ERROR_FATAL); + return RPKI_ERROR; + } + } else { + if (addr.roa6.max_pxlen > IP6_MAX_PREFIX_LENGTH || addr.roa6.max_pxlen < addr.roa6.pxlen) { + RPKI_WARN(cache->p, "Received a corrupted packet from cache server"); + rpki_send_error_pdu(cache, CORRUPT_DATA, pdu->len, pdu, "Corrupted PDU"); + rpki_cache_change_state(cache, RPKI_CS_ERROR_FATAL); + return RPKI_ERROR; + } + } + if (cf->ignore_max_length) { if (type == IPV4_PREFIX) diff --git proto/rpki/rpki.c proto/rpki/rpki.c index ab0837f3..91b69da0 100644 --- proto/rpki/rpki.c +++ proto/rpki/rpki.c @@ -288,9 +288,6 @@ rpki_cache_change_state(struct rpki_cache *cache, const enum rpki_cache_state ne case RPKI_CS_ERROR_FATAL: /* Fatal protocol error occurred. */ - rpki_force_restart_proto(cache->p); - break; - case RPKI_CS_ERROR_TRANSPORT: /* Error on the transport socket occurred. */ rpki_close_connection(cache);

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Incorrect handling of primary/secondary IP address status.
by Alexander 18 Dec '21

18 Dec '21

Hi, Looks like bird (2.0.8 on Linux) incorrectly handles primary/secondary IP address status. For example, this is initial state (output from "show interfaces"): enp6s20 up (index=2 master=switch) MultiAccess Broadcast Multicast AdminUp LinkUp MTU=1500 192.168.111.1/24 (Preferred, scope site) 192.168.111.2/24 (Secondary, scope site) Then I remove 192.168.1.2/24, 192.168.111.2/24 promoted to primary (promote_secondaries is enabled on interface), but bird does not get it: enp6s20 up (index=2 master=switch) MultiAccess Broadcast Multicast AdminUp LinkUp MTU=1500 192.168.111.2/24 (Secondary, scope site) ... while it is actually primary now: 2: enp6s20: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master switch state UP group default qlen 1000 link/ether xx:xx:xx:xx:xx:68 brd ff:ff:ff:ff:ff:ff permaddr xx:xx:xx:xx:xx:30 inet 192.168.111.2/24 scope global enp6s20 valid_lft forever preferred_lft forever From now on, no address within same network will ever get "primary" status until and unless all addresses within this network will be deleted. Looks like it remembers "secondary" status once seen and never updates it. "reload", "configure" and "enable"/"disable" on do not help either. I hit this issue after noticing that OSPF couldn't see neighbors after few changes in IP configuration (as it ignores all secondaries). Best regards, Alexander.

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