Special Forums UNIX and Linux Applications Information on forwarding queue occupation in a Linux router Post 303039947 by i_mll on Friday 18th of October 2019 12:29:31 PM
Information on forwarding queue occupation in a Linux router

Hello.
I have an OpenWrt router forwarding traffic from a network to another and I'm building a monitoring tool that requires information about the packet queue/ ring buffer (in the receiving side/interface - rx) occupation, alerting me when it is close to its maximum capacity.

However, after analysing the following files (linux filesystem):
  • tcp_mem/tcp_rmem/tcp_wmem in /proc/sys/net/ipv4
  • tx_queue_len in /sys/class/net/(interface)
  • sockstat in /proc/net

I concluded these files would only be relevant for my program if the router was the destination or source of the TCP packets, which is not the case. So, as I discussed with a professor of mine, the metrics these files provide are not relevant in a forwarding situation, as the packets do not go to the TCP queues.

If that's true, then where (in what folder/file) can I find information about the router's forwarding queue's current occupation and its maximum occupation, if there's any information on the matter? Note that this question is not limited to the OpenWrt OS, but any linux system.
 
Test Your Knowledge in Computers #575
Difficulty: Medium
If a program has poor memory management and fails to deallocate memory when it is no longer needed, the memory will not leak.
True or False?

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FAITH(4)                                                   BSD Kernel Interfaces Manual                                                   FAITH(4)

NAME
faith -- IPv6-to-IPv4 TCP relay capturing interface SYNOPSIS
device faith DESCRIPTION
The faith interface captures IPv6 TCP traffic, for implementing userland IPv6-to-IPv4 TCP relay like faithd(8). Each faith interface is created at runtime using interface cloning. This is most easily done with the ifconfig(8) create command or using the cloned_interfaces variable in rc.conf(5). Special action will be taken when IPv6 TCP traffic is seen on a router, and the routing table suggests to route it to the faith interface. In this case, the packet will be accepted by the router, regardless of the list of IPv6 interface addresses assigned to the router. The packet will be captured by an IPv6 TCP socket, if it has the IN6P_FAITH flag turned on and matching address/port pairs. As a result, faith will let you capture IPv6 TCP traffic to some specific destination addresses. Userland programs, such as faithd(8) can use this behavior to relay IPv6 TCP traffic to IPv4 TCP traffic. The program can accept some specific IPv6 TCP traffic, perform getsockname(2) to get the IPv6 destination address specified by the client, and perform application-specific address mapping to relay IPv6 TCP to IPv4 TCP. The IN6P_FAITH flag on a IPv6 TCP socket can be set by using setsockopt(2), with level IPPROTO_IPV6 and optname IPv6_FAITH. To handle error reports by ICMPv6, some ICMPv6 packets routed to an faith interface will be delivered to IPv6 TCP, as well. To understand how faith can be used, take a look at the source code of faithd(8). As the faith interface implements potentially dangerous operations, great care must be taken when configuring it. To avoid possible misuse, the sysctl(8) variable net.inet6.ip6.keepfaith must be set to 1 prior to using the interface. When net.inet6.ip6.keepfaith is 0, no packets will be captured by the faith interface. The faith interface is intended to be used on routers, not on hosts. SEE ALSO
inet(4), inet6(4), faithd(8) Jun-ichiro itojun Hagino and Kazu Yamamoto, An IPv6-to-IPv4 transport relay translator, RFC3142. HISTORY
The FAITH IPv6-to-IPv4 TCP relay translator first appeared in the WIDE hydrangea IPv6 stack. BSD April 10, 1999 BSD

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