Re: default route via OSPF depending on the ISP

[Ondrej Zajicek]

On Thu, Dec 03, 2015 at 03:12:10PM +0000, Rohrmann Sascha wrote:
> > Well, you could use static default-route and 'check link' option, but that 
> > will help you only in the third case, not in the second one. 
> > For the second case, you must have some other way to establish whether ISP 
> > is up or down, either by running some routing protocol between 
> > you and ISP, or running BFD session.
> 
> Just as you said, that will only help me in the third case. 
> In which way should BFD be able to accomplish my goal?
> In my understandings BFD only checks if the link is available. If this isn't 
> given, BFD tells Bird this problem.

BFD checks whether specified/destination IP is available (but it also must run 
BFD).
Therefore both link and host must be up.


> Second problem is, not every ISP supports BFD yet because BFD is kinda new. 

That is true, and also BFD-controlled static routes are only in devel version 
of BIRD,
not in v1.5.0


> I was thinking about a simple ping which checks the availability of the 
> opposite party. 
> Am I able to include a simple shell script in bird? 

No


> Do you have more information and/or tips for me, by chance? 

As others wrote, you could do periodic pinging by e.g. fping and enable/disable 
a static protocol
using birdc (birdc disable XXX). See the attached script, which does something 
like that and 
estimating packet loss.


> > I was thinking about the bfd protocol, but bfd is kinda new and you can't 
> > run more than one instance in bird.
> > Well, is there any reason why to run multiple BFD instances in BIRD?
> 
> Well... you could create one bfd instance for one single interface.
> Furthermore you could then check the availability for e.g. my problem instead 
> of checking all BFD instances.

I don't understand here.


-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santi...@crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."

#!/usr/bin/perl

$ip          = 'A.B.C.D';
$logfile     = "/var/log/XXX";
$logfile2    = "/var/log/YYY";
$link_up     = "/usr/sbin/birdc enable XXX";
$link_down   = "/usr/sbin/birdc disable XXX";
$cmd         = 'fping -c 40 -p 50 ' . $ip . ' 2>&1 >/dev/null';


$state = 0;
$start = 1;
$counter = 50;
$tc = 0;

open(LOGFILE, '>>', $logfile);
print LOGFILE localtime () . ': watchdog (' . $ip . ") started\n";
close(LOGFILE);

while (1)
{
    $unreach = `$cmd`;
    $unreach =~ s/.*\/([[:digit:]]+)%.*/\1/s;

    open(LOGFILE2, '>>', $logfile2);

    if ($tc == 0)
    {
	print LOGFILE2 localtime () . ":";
    }

    print LOGFILE2 " " . (0+$unreach) . "%";
    $tc ++;

    if ($tc > 10)
    {
	print LOGFILE2 "\n";
	$tc = 0;
    }

    close(LOGFILE2);


    
    if ($unreach == 0)
    {
	$counter -= 100;
    }
    elsif ($unreach < 3)
    {
    	$counter -= 50;
    }
    elsif ($unreach < 6)
    {
    	$counter -= 10;
    }
    else
    {
	$counter += $unreach;
    }

    if ($counter > 300)
    {
	$counter = 300;
    }
    
    if ($counter < 0)
    {
	$counter = 0;
    }
    
    if ((($start) && ($unreach < 6)) ||
        (($state == 0) && ($counter < 30)))
    {
        system ($link_up);

	$state = 1;
	$start = 0;

	open(LOGFILE, '>>', $logfile);
	print LOGFILE localtime () . ': Link (' . $ip . ") online\n";
	close(LOGFILE);
    }
    if ((($start) && ($unreach >= 6)) ||
        (($state == 1) && ($counter > 95)))
    {
	system ($link_down);

    	$state = 0;
	$start = 0;

	open(LOGFILE, '>>', $logfile);
	print LOGFILE localtime () . ': Link (' . $ip . ") offline\n";
	close(LOGFILE);
    }
    
    sleep 2;
}

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