proxmox repo host behaviour

Spiros Papageorgiou

Well-Known Member
Aug 1, 2017
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Hi all,

A question to Proxmox:
Is it true that download.proxmox.com (the repo host) sends jumbo frames which are fragmented along the way by your routers?

I'm getting fragments which are reassembled at the destination (my proxmox host).

If the above is true, let me tell you about a scenario that took be a day to realize:
I have the proxmox hosts behind a Vyos VM, doing NAT. The Vyos VM is running on vmware.
I tried to apt-get update the proxmox and it was stalling 'waiting for headers'.... A tcpdump showed that the connection was actually open, but when the real data (big packets) was to be sent, nothing really arrived at the Vyos.

To cut the long story-sort, Vmware needed to increase MTU because I was using tagged packets on Vyos. While this is not your problem, your packets from download.proxmox.com did have the DF bit set, because they were fragments. So, while I was able to download anything from other sites, the downloads from download.proxmox.com were stalling forever, because packets were dropped somewere in between (vmware).

I don't really know, if my story is fully accurate, but I thought I should discuss it with you and others. I have seen others reporting about the stalled downloads and blaming "the virtualized firewall" (not necessarily from your host).

Regards,
Spiros

PS: The point where packets were dropped is not clear yet
 
At least not from our download servers, as they use MTU 1500. It could be that the MTU was below 1500, somewhere on the way (Vmware VXLan or similar). Tracepath might be able to discover the mtu or manually walking the path with ping.
 

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