05-31-2007 05:34 AM - edited 03-03-2019 05:14 PM
Hi,
Hi i have an AS number & an IP range supplied by ARIN for my headquarters. I am doing Multi-home with a couple of ISPs & running BGP for this.
I have another office with Internet connectivity in ASIA.
I want to use the same ARIN assigned AS number & an unused ARIN subnet from my Headquarters range for multi-home BGP setup ?
Is this possible.
05-31-2007 06:12 AM
Hi,
Yes you can freely do that, but make sure to use an unused IP subnet in the new location (not advertised from the main office in order to prevent any routing loops).
HTH, please do rate all helpful replies,
Mohammed Mahmoud.
05-31-2007 07:24 AM
Thank you. Can explain me as to how will the routing happen.
How do i have to configure the routing such that traffic intended to my headquarters ( US ) subnets is routed there & the traffic intended to my ASIA subnet is routed to the ASIA network ?
Any Link / details would be greatly appreciated
05-31-2007 08:28 AM
how both the sites are connected with each other...?
what ever i understand is you want to use the same AS number for your USA and ASIA network... it means USA and ASIA network will be in the same AS cloud...right!!!
regards
Devang
05-31-2007 10:40 PM
You understood it right.
Both sites are connected to the Internet using different ISPs
06-01-2007 04:58 AM
i think tunneling will solve your issue... creat the GRE tunnel between your two site and try to send and receive the routing update through that tunnel and get the reachablility between the loopback of each site and then configure the IBGP between both. but during configuration you have to make sure that your asia site traffic should exit through the ISP of the ASIA and same for US... so there you need the routfiltering for outgoing and incoming traffic for the internet... and you have to make sure that only internal subnets of the two different site should be reachable via tunnel...
regards
Devang
06-01-2007 02:52 AM
Hi,
Teoretically this is ok, but you need to
ask the ISP in ASIA the smallest Ip prefix they can advertise. And also think about prefix ISP's accept. It cannot be in the same summarized net, you already annonce. But I believe that you are aware of this.
BR,
Bjornarsb
06-01-2007 03:54 AM
Are you sure about this ?
It cannot be in the same summarized net,
Can i use a /24 which is unused in US from a pool of /18 subnet ?
Let me know if you have any docs for this ?
06-01-2007 05:14 AM
Hi,
I have no docs, this is practical conciderations from an ISP point of view :)
Lets look at this scenario:
ISP1 announces 192.168.0.0/16
with same AS-path.
ISP254 want to announce 192.168.1.0/24
with same as-path.
Ok, then ISP1 actually needs to allow input
of same net as they announce.
ISP policy differ from country to country.
So I'm adviceing you to apply for a second
ip nett and a new AS number.
IP and AS should teoretically and historically correspond with SOO area.
BR,
Bjornarsb
06-01-2007 12:15 PM
Hi Anand,
I've worked a lot with RIRs, but i've never done this before, but basically you should peer with the 2 ISPs in the 2 regions, you should advertise 2 different unsummarized subnet to both ISPs (for example 2 different class Cs to each), this should theoretically work, but i strongly recommend that you contact ARIN, they are the best party that can advise and help you do the best action to have this working according to their policies, and they are really very helpful, please contact them via "hostmaster@arin.net", plus of course arranging with both ISPs.
HTH, please do rate all helpful replies,
Mohammed Mahmoud.
06-03-2007 11:22 PM
Thanks i will do this.
Just an anology -
Is'nt this case similar to Routing.
I advertise a bigger subnet of /18 from one region. Then advertise another subnet of /24 from another region. The Network will identify how to reach each network since the lower mask /24 will advertise specifically to that particular region ?
06-03-2007 11:31 PM
Hi Anand,
Yes it is, but i recommended that you contact your RIR (ARIN) and your ISP, just to make sure that there is no contradiction with the internet routing policies.
HTH, please do rate all helpful replies,
Mohammed Mahmoud.
06-04-2007 12:19 AM
Hi,
In a local AS this is true, but ISP policy is
to not accept a prefix in the range its advertising self. Same is with AS number.
ISP do not accept icomming AS witch is the same as its "owns". This is traditional BGP policies and the reaseon why BGP works.
So I quess that the answer you get is to
do as I have posted, else you could or probarly will get into trouble :)
BR,
Bjornarsb
06-04-2007 01:12 AM
Hi,
The main problem here is the AS-Path, Site 1 will drop received routes from Site 2, since they are originated from the same AS (AS-Path filtering to avoid routing loops), there are many work around, thats why i strongly recommend that you contact ARIN and your ISPs, to agree on the optimum solution for your scenario.
HTH,
Mohammed Mahmoud.
06-04-2007 02:32 AM
I got this info from Cisco IP Journal.
But i am not able to understand whether it can be applicable to AS on the Internet.
Refer the attachment for the Diagram.
Can an ASN Be Split Across Separated Subdomains?
There are many cases of dispersed networks that exist in multiple locations.
If these locations are all administered by a single entity, it may be
desirable to use a single ASN across all these domains. This scenario
is possible, but considerable care needs to be exercised when designing
the routing configuration. Figure 4 shows two distinct subdomains of
AS1, and they are not interconnected internally.
Figure 4: Split AS
AS 1
AS 2 AS 3 AS 4
AS 1
B
192.0.2.128/25
A
192.0.2.0/25
AS1 (A) advertises the prefix 192.0.2.0/25 to AS2, and this advertisement
is propagated to AS2, AS3, and AS4. When AS4 passes this
advertisement to the other segment of AS1 (B), this router rejects the
advertisement because the associated AS path (4, 3, 2, 1) indicates that
the route has already passed through AS1. Similarly, the first segment
of AS1 (A) rejects the advertisement of 192.0.2.128/25 from AS2,
because its path (4, 3, 2, 1) also indicates that a loop has formed. To
restore complete connectivity between the distinct parts of AS1, AS1
needs to configure static routes at its edges. If AS1 (A) configures a
static route to 192.0.2.128/25 pointing toward AS2, and AS1 (B)
similarly configures a route to 192.0.2.0/25 through AS4, then the
configuration enables full connectivity.
In more complex configurations where each of the segments of the
network is multiply connected, the static route configuration becomes
more complex. However, with very careful configuration, a single ASN
can be distributed across multiple distinct networks.
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