Re: Best practice for redundancy when there're more than 2x ISP

Hi John,

Thanks for your recommendation. You got it right on my requirements.

Lets me try to inteprete your solution:

> Primary ISP1 ^ISP1AS_[0-9]*$ = 250
> Primary ISP2 ^ISP2AS_[0-9]*$ = 200
> Backup ISP1 ^ISP1AS_[0-9]*$ = 150

Since you did not mention how you set up local preference for the rest
of the Interet, all other routes get default Pref of 100, including
routes from ISP2 & its customers via the backup link.

Backup ISP2 ^ISP2AS_[0-9]*$ = 100

Rest of Internet (received from all links) = 100

Here's the catches:

- Total outgoing traffic for ISP1, ISP2, and their direct customers
account for less than 10% of the total Internet (while total number of
prefixes of these two ISPs probaly only account for less than 0.01% of
the full BGP table). Your manupulation will only target very small
portion, and left the mijority of destinations un-controlled !!!

- For the rest of Internet destination, default Local Preference is
100 for all 4 links. You will see traffic going via the backup ISP1 as
well as backup ISP2 even in normal situation. This totally breaks one
of my requirements: no traffic falls on any backup links, if their
primary link is working.

Looking forward to a better recommendation.

On Fri, Sep 24, 2010 at 8:44 AM, Edward John
<edwardjohn2020_at_googlemail.com> wrote:
> Hi TechGuy,
> As I understood your case:
> You want share the o/b traffic even if there is failure in one Primary ISP
> link.
> ie:
> If primary ISP1 fail - traffic to be balanced between backup ISP1 & primary
> ISP2
> If primary ISP2 fail - traffic to be balanced between primary ISP1 & backup
> ISP2
>
> If so, I will use the following method:
> Assign high local preference for the routes received from corresponding ISP
> and its directly peered AS.
> For example:
> Primary ISP1 ^ISP1AS_[0-9]*$ = 250
> Primary ISP2 ^ISP2AS_[0-9]*$ = 200
> Backup ISP1 ^ISP1AS_[0-9]*$ = 150
>
> By this you can some what share traffic between the links, but
> never guarantee the symmetrical path.
> Regards,
> John
>

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