Richard,
Yes I am referring eBGP scenario. I suggest distance calculations based on
1. ICMP delay between eBGP speakers.
2. Manually configure binding to remote AS.
Each eBGP speaking routers need to accumulate distance value when advertised
routes to external peer.There is no reqirment to synchronize different
administrative domains since router itself automatically calculate value and
add when routes advertised similar to AS PATH addition operation.
----- Reply message -----
From: "Richard Li" <renwei...@huawei.com>
To: "Duleep Thilakarathne" <dule...@mobitel.lk>, "UTTARO, JAMES"
<ju1...@att.com>, "'Robert Raszuk'" <rob...@raszuk.net>
Cc: "'bess@ietf.org'" <bess@ietf.org>
Subject: [bess] BGP route selection criteria - geographic distance when AS_PATH
are equal
Date: Fri, Aug 7, 2015 10:11 PM
There might be a good point here. RFC 7311 only takes care of the IGP metrics.
But In Duleep’s example, the metrics between two eBGP speakers are not taken
into consideration. In order to have AIGP attribute to really represent the
accumulated one, the metrics on such links should be considered as well.
However, there might be some challenges or obstacles: The way to configure one
metrics on the link between two eBGP speakers might not be consistent with the
way to configure another metrics on the another link between two speakers.
Richard
From: BESS [mailto:bess-boun...@ietf.org] On Behalf Of Duleep Thilakarathne
Sent: Friday, August 07, 2015 8:41 AM
To: UTTARO, JAMES; 'Robert Raszuk'
Cc: 'bess@ietf.org'
Subject: Re: [bess] BGP route selection criteria - geographic distance when
AS_PATH are equal
Jim,
What I want to suggest is to insert item 5 (refer below items listed) to BGP
best path selection algorithm. Once AS-PATH length is equal, next we can think
on how to select best outgoing interface. If we don’t select proper outgoing
interface it will affect to latency. I am talking this based on practical
experience I have in ISP environment. There are several options to select best
outgoing interface when AS-PATH are equal. In this case I suggest geo distance
to destination. Following are options to calculate geo distance. Router selects
outgoing interface with lowest GEO distance to destination.
1. BGP speaking router can add distance when advertise to route to upstream
similar to AS-PATH attribute. For example
A----B----C-----D
Router B advertise distance AB to router C. router C advertise accumulated
distance AB+BC to router D.
2. Above distance can be configured as manual interface command or dynamically
using ICMP or similar mechanism. We can assume ICMP delay propositional to geo
distance.
3. Alternative option is to calculate real geo distance from coordinate system.
In this case we miss intermediate hops. Accuracy is not much accurate since
cable paths do not follow real coordinate based distance. In this case we
should have knowledge on coordinates of upstream router which relevant IP block
advertise.
Option 1 can be achieved through BGP protocol itself ,if agreed to introduce
new attribute.
Option 3 more suitable to SDN based implementation. Calculation can be daily or
weekly basis as this is not primary criteria.
Further Consider following scenario.
I am in Sri Lanka. Assume I have upstream POPS to Singapore, AMS, New York.
Assume I need to reach destination IP located at Japan. When I check BGP
routing table, AS-PATH length is equal from all three upstream. Then I have
three options. Then router selects any interface randomly if no policy
configured. I hope you agreed up to this point. In such case I suggest to
consider GEO distance to destination. In most cases lowest distance path is the
best path. This may not correct always but better than random outgoing
interface selection.
1. Discarding the routes with the unreachable Next_Hop.
2. Preferring the route with the highest Local_Pref.
3. Preferring the aggregated route. The preference of an aggregated route is
higher than the preference of a non-aggregated route.
4. Preferring the route with the shortest AS-Path.
5. If AS-Path finds equal, consider shortest GEO distance. If still distance is
same follow next steps.
6. Comparing the Origin attribute and selecting the routes with the Origin
attribute as IGP, EGP, or Incomplete in order.
Regards
Duleept
From: UTTARO, JAMES [mailto:ju1...@att.com]
Sent: Friday, August 7, 2015 7:44 PM
To: Duleep Thilakarathne; 'Robert Raszuk'
Cc: 'bess@ietf.org'
Subject: RE: [bess] BGP route selection criteria - geographic distance when
AS_PATH are equal
Duleep,
So a bit confused here.
How do want the decision making to go if a path has a shorter
AS-PATH and longer latency than the alternative?? If latency is the prime
motivator why do you care about AS-PATH length at all.. Comments In-Line..
Jim Uttaro
From: Duleep Thilakarathne [mailto:dule...@mobitel.lk]
Sent: Friday, August 07, 2015 9:31 AM
To: Robert Raszuk
Cc: UTTARO, JAMES; bess@ietf.org<mailto:bess@ietf.org>
Subject: RE: [bess] BGP route selection criteria - geographic distance when
AS_PATH are equal
Hi Raszuk,
Question 1: How does the router know about user's high latency ?
Actually I am referring ISP edge router to another ISP edge router delay due to
transmission distance.
[Jim U>] The underlying facility and it’s representative transmission distance
will most likely differ from geographical distance. Which do you want to
address? To Robert’s point you still need to acquire that knowledge and it may
be orthogonal to an attribute that is defined as delay.
Question 2: How do you assure Internet stability where you start churning paths
based on the latency of data plane ?
It is not required to consider stability in this situation since it is
unavoidable. What is refer is, router need to select best outgoing path
considering physical distance whenever possible when AS-PATH length is equal.
If router selects long distance path randomly, it impacts to latency.
Question 3: What you are after has effectively been solved many years ago .. it
is called Optimized Edge Routing (OER) / Performance Routing (PFR) - I suggest
you google for those terms.
Thank for the suggestion. I gone through these proposals. But what I am
suggesting is whether we can address this idea from BGP protocol level. For
example by introducing new attribute related to physical distance/delay similar
to AS-PATH. New attribute need to update across the As path. My ultimate
objective is to prevent router randomly select outgoing path when AS-PATH
lengths are equal. Further I am trying SDN based simulation these days. Hope I
can share output. But this could similar to what you have proposed except geo
distance calculation mechanism.
Refer below standard BGP route selection criteria. I suggest item 5. Wordings
may different from vendor to vendor.
1. Discarding the routes with the unreachable Next_Hop.
2. Preferring the route with the highest Local_Pref.
3. Preferring the aggregated route. The preference of an aggregated route is
higher than the preference of a non-aggregated route.
4. Preferring the route with the shortest AS-Path.
5. If AS-Path finds equal, consider shortest GEO distance. If still distance is
same follow next steps.
6. Comparing the Origin attribute and selecting the routes with the Origin
attribute as IGP, EGP, or Incomplete in order.
Regsrds
Duleept
From: rras...@gmail.com<mailto:rras...@gmail.com> [mailto:rras...@gmail.com] On
Behalf Of Robert Raszuk
Sent: Friday, August 7, 2015 6:29 PM
To: Duleep Thilakarathne
Cc: UTTARO, JAMES; bess@ietf.org<mailto:bess@ietf.org>
Subject: Re: [bess] BGP route selection criteria - geographic distance when
AS_PATH are equal
Duleep,
> Then end user experiences high latency to reach destination. In such
> a case, I suggest router need to consider geographic distance to
> destination and select path via NTT to reach destination by default.
Question 1: How does the router know about user's high latency ?
Question 2: How do you assure Internet stability where you start churning paths
based on the latency of data plane ?
Question 3: What you are after has effectively been solved many years ago .. it
is called Optimized Edge Routing (OER) / Performace Routing (PFR) - I suggest
you google for those terms.
Regards,
R.
On Fri, Aug 7, 2015 at 2:51 PM, Duleep Thilakarathne
<dule...@mobitel.lk<mailto:dule...@mobitel.lk>> wrote:
Hi Jim,
Please refer below example.
Assume destination IP is in Asian region. Particular ISP in a different
location (Say India) has upstream peering to US POP (Say AT&T) and Asia POP
(Say NTT). If we check BGP routing table, assume it shows
XX.XX.XX.XX/24 -------->AS - AT&T,AS-XX,AS-Destination
-------->AS - NTT,AS-YY,AS-Destination
In above case AS-PATH is equal and assume router automatically select path via
AT&T. Then end user experiences high latency to reach destination. In such a
case, I suggest router need to consider geographic distance to destination and
select path via NTT to reach destination by default. Deciding geo distance is a
challenge but there are options. Here geo distance means shortest distance to
reach IP destination from upstream POP. Current practice is to use community
strings, but it depends on upstream ISP capability.
Can you comment my idea.
Regards
Duleept
From: UTTARO, JAMES [mailto:ju1...@att.com<mailto:ju1...@att.com>]
Sent: Friday, August 7, 2015 4:09 PM
To: Duleep Thilakarathne; 'Robert Raszuk'
Cc: 'bess@ietf.org<mailto:bess@ietf.org>'
Subject: Re: [bess] BGP route selection criteria - geographic distance when
AS_PATH are equal
Duleep,
Assuming AS-PATH is equal and AS-Content different how can you
know that the internal metrics of each AS are consistent and mirror actual
geographic distances? You have to be assured that each administrative domain
applies the same metric assignment. I do not believe this is possible when
there are multiple administrative domains.
Jim Uttaro
From: BESS [mailto:bess-boun...@ietf.org] On Behalf Of Duleep Thilakarathne
Sent: Friday, August 07, 2015 5:19 AM
To: Robert Raszuk
Cc: bess@ietf.org<mailto:bess@ietf.org>
Subject: Re: [bess] BGP route selection criteria - geographic distance when
AS_PATH are equal
Hi Raszuk,
I went through RFC7311 and my concern is different than RFC 7311. I have
analyzed full BGP routing table (541,199 routes) with two tier 1 ISP
multi-homing scenario and found nearly 50% of routes have equal AS-PATH length.
In this analysis It was considered, there was no route policy applied to
influence local preference. According to BGP best path selection algorithm,
when AS-PATH lengths are equal, router breaks tie condition based on route
internal logic. This does not grantee proper outgoing path selection.
Appreciate your concern on above analysis.
Regards
Duleept
From: Robert Raszuk [mailto:rob...@raszuk.net]
Sent: Monday, July 27, 2015 2:40 AM
To: Duleep Thilakarathne
Cc: bess@ietf.org<mailto:bess@ietf.org>
Subject: Re: [bess] BGP route selection criteria - geographic distance when
AS_PATH are equal
Hi Duleep,
Please consider RFC 7311 and provide feedback why you think it is not
sufficient for your objective.
https://tools.ietf.org/html/rfc7311
Best,
R.
On Sun, Jul 26, 2015 at 9:15 PM, Duleep Thilakarathne
<dule...@mobitel.lk<mailto:dule...@mobitel.lk>> wrote:
Hi,
I would like to suggest to consider geographic distance when AS_PATH are equal
in BGP route selection criteria. (as tie breaking rule). Can anybody comment on
my idea.
Regards
Duleept
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