[c-nsp] Anycast Questions

Tue Feb 15 03:48:17 EST 2011

Hi Guys,

Has anyone had experience with or knowledge of IP Anycast?

I am a little confused as to how the advertisement of the same Anycast
address is possible at different routers in the network at possibly separate
locations. Let's say I have a web service and I would like to Anycast the
service to my national organisation with the help of my IGP. Am I right in
thinking that each site location that has an instance of the Anycast service
would need to advertise this Anycast address (typically a host route) into
the routing table, and that routers within the organisation will simply use
the mechanics of the routing protocol to direct client communication to the
Anycast service via the best path or route? 

Is the idea that the host route being advertised will have a longer match
than any potential summarised network that may cover the range of Anycast IP
addresses used? Is this why it is preferred to have a dedicated network that
is not summarised at any point in the network to advertise Anycast services?

I guess when it came to Anycast services over the Internet It would be
fairly simple process to advertise your own Anycast addresses at any of your
border routers around the world and AS-PATH would take care of the rest?

Can someone clarify these points or am I completely off track?

Thanks,

-Aaron

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Yann GAUTERON
Sent: Tuesday, 15 February 2011 1:30 PM
To: Mark Tees; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] "continue" clause in route-maps

Hi Mark,

I forgot to mention that I did try both syntaxes:
* "continue" alone
* "continue" followed by a seq number ("continue 20" in the present case).

Thanks for your feedback.
Y.

2011/2/14 Mark Tees <marktees at gmail.com>

> Hi,
>
> I had this working at one point in time on a 7200 series (dunno which IOS)
> but my config was with 'continue' pointing to a specific rule:
>
>  route-map TRANSIT-OUT permit 10
>  match community MATCH_INTERNAL
> * continue 20
>  set comm-list MATCH_INTERNAL delete
>
> Good luck!
>
>
>
> On 15/02/11 6:03 AM, Yann GAUTERON wrote:
>
>> Hi !
>>
>> I would like to apply some sophisticated rules with my prefixes announced
>> with BGP.
>>
>> I saw that Cisco implemented a "continue" clause that could permit me to
>> achieve my goal.
>>
>> Before implemented such rules on my productive routers, I did some tests
>> with GNS3, but it seems that the "continue" does not work !
>>
>> For a simple simulation with 2 routers (in BGP AS 1 and AS 2), I cannot
>> see
>> the expected result.
>>
>> Configuration on the router in AS1:
>> ip cef
>> !
>> interface Loopback0
>>  ip address 1.1.1.1 255.255.255.255
>> !
>> interface GigabitEthernet1/0
>>  ip address 10.0.0.1 255.255.255.0
>>  negotiation auto
>> !
>> router bgp 1
>>  no synchronization
>>  bgp log-neighbor-changes
>>  network 1.0.0.0 route-map NET-1-0-0-IN
>>  neighbor 10.0.0.2 remote-as 2
>>  neighbor 10.0.0.2 send-community
>>  neighbor 10.0.0.2 route-map PEER-OUT out
>>  no auto-summary
>> !
>> ip forward-protocol nd
>> ip route 1.0.0.0 255.0.0.0 Null0
>> !
>> ip bgp-community new-format
>> ip community-list 1 permit 1:1
>> !
>> route-map PEER-OUT permit 10
>>  match community 1
>>  continue
>>  set community 1:100 additive
>> !
>> route-map PEER-OUT permit 20
>>  set community 1:200 additive
>> !
>> route-map NET-1-0-0-IN permit 10
>>  set community 1:1 1:2 65000:1 65000:2
>>
>> With this configuration, I would expect my second router (in AS 2), to
>> receive the prefix 1.0.0.0/8 with the communities 1:1 1:2 1:100 1:200
>> 65000:1 65000:2.
>>
>> But I cannot see 1:200 in my communities:
>> Router#sh ip bgp 1.0.0.0
>> BGP routing table entry for 1.0.0.0/8, version 9
>> Paths: (1 available, best #1, table Default-IP-Routing-Table)
>> Flag: 0x820
>>   Not advertised to any peer
>>   1
>>     10.0.0.1 from 10.0.0.1 (1.1.1.1)
>>       Origin IGP, metric 0, localpref 100, valid, external, best
>>       Community: 1:1 1:2 1:100 65000:1 65000:2
>>
>> My GNS3 router is a 7200 and has IOS 12.4(25d). My productive router is a
>> 7600 with 12.2(33)SRE, but I cannot emulate a 7600 on GNS3 !
>>
>> Is the problem due to a misbehaviour of that IOS 12.4(25d) on my
"virtual"
>> 7200, or did I miss something with the way "continue" do work ? Is it a
>> misbehavior I would face with my productive 7600 ?
>>
>> Thanks!
>>
>> Yann
>>
>>
>>
>> Router#sh ver
>> Cisco IOS Software, 7200 Software (C7200-P-M), Version 12.4(25d), RELEASE
>> SOFTWARE (fc1)
>> Technical Support: http://www.cisco.com/techsupport
>> Copyright (c) 1986-2010 by Cisco Systems, Inc.
>> Compiled Wed 18-Aug-10 11:54 by prod_rel_team
>>
>> ROM: ROMMON Emulation Microcode
>> BOOTLDR: 7200 Software (C7200-P-M), Version 12.4(25d), RELEASE SOFTWARE
>> (fc1)
>>
>> Router uptime is 14 minutes
>> System returned to ROM by unknown reload cause - suspect
>> boot_data[BOOT_COUNT] 0x0, BOOT_COUNT 0, BOOTDATA 19
>> System image file is "tftp://255.255.255.255/unknown"
>>
>> Cisco 7206VXR (NPE400) processor (revision A) with 245760K/16384K bytes
of
>> memory.
>> Processor board ID 4294967295
>> R7000 CPU at 150MHz, Implementation 39, Rev 2.1, 256KB L2 Cache
>> 6 slot VXR midplane, Version 2.1
>>
>> Last reset from power-on
>>
>> PCI bus mb0_mb1 (Slots 0, 1, 3 and 5) has a capacity of 600 bandwidth
>> points.
>> Current configuration on bus mb0_mb1 has a total of 600 bandwidth points.
>> This configuration is within the PCI bus capacity and is supported.
>>
>> PCI bus mb2 (Slots 2, 4, 6) has a capacity of 600 bandwidth points.
>> Current configuration on bus mb2 has a total of 0 bandwidth points
>> This configuration is within the PCI bus capacity and is supported.
>>
>> Please refer to the following document "Cisco 7200 Series Port Adaptor
>> Hardware Configuration Guidelines" on Cisco.com<http://www.cisco.com>
>> for c7200 bandwidth points oversubscription and usage guidelines.
>>
>>
>> 1 FastEthernet interface
>> 1 Gigabit Ethernet interface
>> 125K bytes of NVRAM.
>>
>> 65536K bytes of ATA PCMCIA card at slot 0 (Sector size 512 bytes).
>> 8192K bytes of Flash internal SIMM (Sector size 256K).
>> Configuration register is 0x2102
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>
>
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