topic Re: Poor multicast over Tunnel in Routing and SD-WAN

Poor multicast over Tunnel

KGrev — Thu, 26 Oct 2023 13:40:20 GMT

Hi,

I have a cellular router (IR809G) with a tunnel setup. I'm trying to view a multicast video over that tunnel. It does appear but the video quality is very poor. I'm in a great reception area and speed tests from the router into the network hover around ~50meg. The video file is 480p mp4. Other paths from the core router(rp) can view this feed fine but the path through the tunnel is the issue. Are there any requirements for a tunnel connection for multicast to flow properly? Ive attached some details from the spoke and core routers. I hope it is helpful.

Is it interesting that the tunnel does not show a DR for pim? My other pim interfaces on the router do show DR (they are removed from the text)

Thank you for any advice.

Re: Poor multicast over Tunnel

Joseph W. Doherty — Thu, 26 Oct 2023 13:54:14 GMT

Possible tunnel IP fragmentation?

Re: Poor multicast over Tunnel

KGrev — Thu, 26 Oct 2023 14:02:27 GMT

i was thinking so also but i believe the output shows I have the tunnel set to below what it actually is. I also tried useing path detection on the tunnel but go no change. I also tried changing my mtu on my VLC video feed source to 1000-1200. The client at the other end of the tunnel can see this change in wireshark.

Re: Poor multicast over Tunnel

Joseph W. Doherty — Thu, 26 Oct 2023 17:22:47 GMT

I believe, generally, video doesn't do PMTUD.

If you've doing WireShark at the tunnel end, that should show whether there's any fragmentation happening.

Fragmentation is just one common problem with tunnels, but as video is sensitive to network quality, there's many possible issues.

Re: Poor multicast over Tunnel

KGrev — Thu, 26 Oct 2023 18:34:57 GMT

@Joseph W. Doherty I attached two pictures from Wireshark. Do these look dire?

Re: Poor multicast over Tunnel

Joseph W. Doherty — Thu, 26 Oct 2023 20:06:50 GMT

Fyi: unable to view attachments, at the moment (technical issues). Might be several days before I can view them.

Re: Poor multicast over Tunnel

KGrev — Thu, 26 Oct 2023 20:15:08 GMT

@Joseph W. Dohertydoes this help?

Re: Poor multicast over Tunnel

Joseph W. Doherty — Thu, 26 Oct 2023 21:41:17 GMT

Yes, it does, thanks!

Unless I'm mistaken, appears there is fragmentation.

You did note you reduced MTU at video source?

Re: Poor multicast over Tunnel

KGrev — Thu, 26 Oct 2023 21:46:25 GMT

@Joseph W. Doherty I'll try to get another picture tomorrow, but if I reduce the mtu size of my video stream at the source, I can see the mtu size has lowered in Wireshark but I still see the fragment messages. I'll try to get another image tomorrow.

Re: Poor multicast over Tunnel

KGrev — Tue, 31 Oct 2023 12:59:09 GMT

@Joseph W. Dohertysorry it has taken me so long. I've been very sick. I'm back at the office today so I hope to reach back to you soon.

Re: Poor multicast over Tunnel

KGrev — Wed, 01 Nov 2023 13:05:58 GMT

@Joseph W. DohertyWhat sort of MTU would you suggest for the tunnel for this setup?

I think the interesting ports here would be:
Cell Router: -Cell0, Tunnel, VPN? Gig0

Internal router - tunnel 10 (outgoing interface is 1500.

Re: Poor multicast over Tunnel

Joseph W. Doherty — Wed, 01 Nov 2023 13:12:00 GMT

Largest that can transit, end-to-end, without being fragmented.

Re: Poor multicast over Tunnel

KGrev — Wed, 01 Nov 2023 13:18:59 GMT

@Joseph W. Dohertyso should I send "dont fragment" pings outside of the tunnel and find my largest mtu then go down from there?

Re: Poor multicast over Tunnel

Joseph W. Doherty — Wed, 01 Nov 2023 14:21:32 GMT

If you knew tunnel overhead, that might do.

You're unable to send DF tagged packet through tunnel?

Re: Poor multicast over Tunnel

KGrev — Wed, 01 Nov 2023 14:39:27 GMT

@Joseph W. DohertySorry i was thinking I should know what size I had to work with then adjust my tunnel to fit within that? Is that the wrong way to go about it?

Re: Poor multicast over Tunnel

Joseph W. Doherty — Wed, 01 Nov 2023 15:41:06 GMT

What you want to accomplish is any traffic that will transit the tunnel will not be fragmented.

How that is accomplished, varies, including setting MTU at source.

Re: Poor multicast over Tunnel

KGrev — Wed, 01 Nov 2023 16:01:59 GMT

@Joseph W. Doherty Here is what I have on the router currently.

interface Tunnel10
description LTE_10_to_4500X
bandwidth 10000
ip address 10.2.55.2 255.255.255.252
no ip redirects
no ip unreachables
no ip proxy-arp
ip mtu 1430
ip pim sparse-mode
ip tcp adjust-mss 1400
ip ospf message-digest-key 1 md5 7 xxxxxxxxx
ip ospf 10 area 0
tunnel source Loopback0
tunnel destination 10.2.5.130
end
!
interface Cellular0
ip address negotiated
ip access-group ACL-INFRASTRUCTURE in
ip access-group ACL-INFRASTRUCTURE out
no ip redirects
no ip unreachables
no ip proxy-arp
encapsulation slip
ip tcp adjust-mss 1460
dialer in-band
dialer idle-timeout 0
dialer string lte
dialer watch-group 1
async mode interactive
crypto ipsec client ezvpn TEST

The other end of the tunnel matches.

Whats weird is the video stream can be changed down to a very small video with mtu 1000. When I wirshark the client on the distant end of the tunnel, I can clearly see packet length of 982 with fragmentation. I can also set the stream to 1340 and see packets with length 1358 with fragmentation.

Re: Poor multicast over Tunnel

Joseph W. Doherty — Wed, 01 Nov 2023 17:48:25 GMT

I don't understand exactly what's happening. A tunnel within a tunnel?

Your MTU and adjust-mss settings don't make sense even without possibly tunneling within another tunnel.

If the transit path has (or may have) a restriction within a restriction, you want to configure for that too.

Your Wireshark results do appear odd, but probably explainable if we correctly understood how transit packets are being treated.

I can explain in general, including using examples, how to configure for "hits" to MTU, but cannot provide specifics without specific information.

What you could try is removing you IP MTU settings, and use an extended ping, using sizes from 500 to 1500, in increments of 100, and examine Wireshark results.

Re: Poor multicast over Tunnel

KGrev — Wed, 01 Nov 2023 18:00:36 GMT

@Joseph W. DohertyThese routers are using an older vpn setup called EZVPN. It doesn't allow multicast by default. So I'm having to tunnel through that vpn just for multicast. I've always struggled with understanding how to adjust mtu so any help is greatly appreciated.

When I remove the mtu settings should I remove them from the tunnel and the Cellular interface? Also should I ping from the local tunnel ip to the distant tunnel ip "10.2.55.1"?

Thank you for your help

Re: Poor multicast over Tunnel

KGrev — Wed, 01 Nov 2023 20:00:19 GMT

@Joseph W. Doherty So I have removed all mtu/mss settings from the tunnel and cellular interface and sent incrementing pings with df from a laptop through the tunnel and from the cellular router tunnel ip to the internal router tunnel ip. Here are my results:

cellular router tunnel ip local to tunnel ip distant(inside): Fragmentation starts at 1477, they are passed at 1476

at the same time, the laptop ping will fail after 1448, Wireshark shows anything higher than that as "no response" then shows fragmentation at exactly 1473.

I hope this is helpful