At 18:15 we were notifed that BGP sessions towards one of our upstream providers went down.
This caused some network dips for one of our core routers while routes were being rebuilt.
At 18.21 the BGP sessions towards upstream was restored.
We’ve asked upstream to investigat the unannounced loss of session.
19.00 Update: Upstream has replied and said that a high CPU situation on their router caused BGP sessions to ”flap” (disconnect and reconnect). The cpu usage is now stable and BGP sessions too.
notified that there is a new remote crash vulnerability many Linux systems .
The CVE has yet to be publicly released, it has just been reserved so far: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11477
The register has published more details: https://www.theregister.co.uk/2019/06/17/linux_tcp_sack_kernel_crash/
Other cloud hosting vendors have published steps on how to mitigate this flaw
and so is Adminor AB.
A patch to linux kernel will be issued by different vendors, meanwhile a
mitigation of these attacks is to disable tcp_sack (tcp selective
It’s possible that the recent reboot of systems already have mitigation for
this exploit but we have not been notified of such by upstream vendor as the
exploit is still not entirely released.
We recommend that you disable tcp_sack as a pre-caution.
TCP sack is used to speed up TCP transfer by allowing computers to tell the
server how much data is left to be sent. This should have minimal impact on
normal operations but we still recommend monitoring for any negative
run which should not require a system reboot:
echo 0 > /proc/sys/net/ipv4/tcp_sack
To make the change persistent across reboots a command such as the following
can be run:echo
’net.ipv4.tcp_sack = 0’ >> /etc/sysctl.conf
We recommend enabling tcp_sack when a kernel patch has been issued and system
Please let us know if you need assistance .