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Re: App fails when rebuilt with newer library, but only when MTU is small
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From: Cristian Rodríguez via curl-library <curl-library_at_lists.haxx.se>
Date: Wed, 5 Oct 2022 11:29:40 -0300
On Wed, Oct 5, 2022 at 11:15 AM Mark Fanara via curl-library
<curl-library_at_lists.haxx.se> wrote:
> The problem turned out to be the fact that an upstream device was sending ICMP ‘fragmentation needed’ back to me with a MTU next hop value < 576. My newer OS apparently discarded them because of the next hop value. I was able to change the OS path MTU behavior by setting /proc/sys/net/ipv4/ip_no_pmtu_disc to 1 (echo ‘1’ > /proc/sys/net/ipv4/ip_no_pmtu_disc) per https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html.
Doing this will cause more trouble than what it is "solving". Unless
you know exactly what you are doing and are well versed on what the
linux kernel will actually do (i.e what the source code does.. and not
what you interpret the documentation to do) do not fiddle with this
settings and expect things to work.
Anyways, this is not a Curl issue. Most of the time you do not want to
change the MTU at all but use MSS clamping instead.
take care.
Date: Wed, 5 Oct 2022 11:29:40 -0300
On Wed, Oct 5, 2022 at 11:15 AM Mark Fanara via curl-library
<curl-library_at_lists.haxx.se> wrote:
> The problem turned out to be the fact that an upstream device was sending ICMP ‘fragmentation needed’ back to me with a MTU next hop value < 576. My newer OS apparently discarded them because of the next hop value. I was able to change the OS path MTU behavior by setting /proc/sys/net/ipv4/ip_no_pmtu_disc to 1 (echo ‘1’ > /proc/sys/net/ipv4/ip_no_pmtu_disc) per https://www.kernel.org/doc/html/latest/networking/ip-sysctl.html.
Doing this will cause more trouble than what it is "solving". Unless
you know exactly what you are doing and are well versed on what the
linux kernel will actually do (i.e what the source code does.. and not
what you interpret the documentation to do) do not fiddle with this
settings and expect things to work.
Anyways, this is not a Curl issue. Most of the time you do not want to
change the MTU at all but use MSS clamping instead.
take care.
-- Unsubscribe: https://lists.haxx.se/listinfo/curl-library Etiquette: https://curl.se/mail/etiquette.htmlReceived on 2022-10-05