From: Pavel Bykov (slidersv@gmail.com)
Date: Mon Jan 12 2009 - 11:22:38 ARST
Great examples Ivan!
On Mon, Jan 12, 2009 at 11:53 AM, Ivan Walker <ivan@itpro.co.nz> wrote:
> Hi Praveen,
>
> local-as : the AS that the router is masquerading as is prepended to
> incoming routes and prepended to outgoing routes following the configured
> AS
> no-prepend: the AS that the router is masquerading as is no longer
> prepended to incoming routes
> replace-as: the AS that the router is configured with as is no longer
> prepended to outgoing routes - only the AS that the router is
> masquerading as is prepended
> dual-as: allow the neighbor to use the configured as or the AS that the
> router is masquerading as
>
> the following should help illustrate
>
> R1 Initial Config:
> ==================
> interface Loopback0
> ip address 1.1.1.1 255.255.255.0
> interface FastEthernet0/0
> ip address 12.12.12.1 255.255.255.0
> router bgp 111
> bgp router-id 1.1.1.1
> no bgp default ipv4-unicast
> bgp log-neighbor-changes
> neighbor 12.12.12.2 remote-as 222
> neighbor 12.12.12.2 version 4
> address-family ipv4
> neighbor 12.12.12.2 activate
> no auto-summary
> no synchronization
> network 1.1.1.0 mask 255.255.255.0
> exit-address-family
>
> R2 Initial Config:
> ===================
> interface Loopback0
> ip address 2.2.2.2 255.255.255.0
> interface FastEthernet0/0
> ip address 12.12.12.2 255.255.255.0
> router bgp 222
> bgp router-id 2.2.2.2
> no bgp default ipv4-unicast
> bgp log-neighbor-changes
> neighbor 12.12.12.1 remote-as 111
> neighbor 12.12.12.1 version 4
> address-family ipv4
> neighbor 12.12.12.1 activate
> no auto-summary
> no synchronization
> network 2.2.2.0 mask 255.255.255.0
> exit-address-family
>
> R1#show ip bgp 2.2.2.0
> BGP routing table entry for 2.2.2.0/24, version 9
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 222
> 12.12.12.2 from 12.12.12.2 (2.2.2.2)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> R2#show ip bgp 1.1.1.0
> BGP routing table entry for 1.1.1.0/24, version 3
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 111
> 12.12.12.1 from 12.12.12.1 (1.1.1.1)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> ++++++++++++++++++++++local-as+++++++++++++++++++++++++++++++
>
> R1 to masquerade as AS666
> R1(config-router)# neighbor 12.12.12.2 local-as 666
>
> R2 updated to peer with AS666
> R2(config-router)# neighbor 12.12.12.1 remote-as 666
>
> R1#show ip bgp 2.2.2.0
> BGP routing table entry for 2.2.2.0/24, version 3
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 666 222
> 12.12.12.2 from 12.12.12.2 (2.2.2.2)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> R2#show ip bgp 1.1.1.0
> BGP routing table entry for 1.1.1.0/24, version 17
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 666 111
> 12.12.12.1 from 12.12.12.1 (1.1.1.1)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> ++++++++++++++++++++++no-prepend+++++++++++++++++++++++++++++++
>
> R1(config-router)# neighbor 12.12.12.2 local-as 666 no-prepend
>
> R1#show ip bgp 2.2.2.0
> BGP routing table entry for 2.2.2.0/24, version 5
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 222
> 12.12.12.2 from 12.12.12.2 (2.2.2.2)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> R2#show ip bgp 1.1.1.0
> BGP routing table entry for 1.1.1.0/24, version 19
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 666 111
> 12.12.12.1 from 12.12.12.1 (1.1.1.1)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> ++++++++++++++++++++++replace-as+++++++++++++++++++++++++++++++
>
> R1(config-router)# neighbor 12.12.12.2 local-as 666 no-prepend replace-as
>
> R1#show ip bgp 2.2.2.0
> BGP routing table entry for 2.2.2.0/24, version 7
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 222
> 12.12.12.2 from 12.12.12.2 (2.2.2.2)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> R2#show ip bgp 1.1.1.0
> BGP routing table entry for 1.1.1.0/24, version 21
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 666
> 12.12.12.1 from 12.12.12.1 (1.1.1.1)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> ++++++++++++++++++++++dual-as+++++++++++++++++++++++++++++++
>
> R2(config-router)#neighbor 12.12.12.1 remote-as 111
> [R2] %BGP-3-NOTIFICATION: sent to neighbor 12.12.12.1 2/2 (peer in wrong
> AS) 2 bytes 029A
> [R2] FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 002D 0104 029A 00B4 0101 0101
> 1002 0601 0400 0100 0102 0280 0002 0202 00
>
> R1(config-router)# neighbor 12.12.12.2 local-as 666 no-prepend replace-as
> dual-as
> [R2] %BGP-5-ADJCHANGE: neighbor 12.12.12.1 Up
>
> R1#show ip bgp 2.2.2.0
> BGP routing table entry for 2.2.2.0/24, version 9
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Not advertised to any peer
> 222
> 12.12.12.2 from 12.12.12.2 (2.2.2.2)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> R2#show ip bgp 1.1.1.0
> BGP routing table entry for 1.1.1.0/24, version 23
> Paths: (1 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x820
> Not advertised to any peer
> 111
> 12.12.12.1 from 12.12.12.1 (1.1.1.1)
> Origin IGP, metric 0, localpref 100, valid, external, best
>
> Ivan
>
>
>
> > Hi GS,
> >
> > Need some help in BGP local-AS parameter?
> >
> > I tried it in my lab without any problem but not able to understand the
> > difference between No-prepend, Replace-as and dual-as parameter.
> >
> > Thanks
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
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>
>
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>
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>
>
>
>
>
>
>
-- Pavel Bykov ---------------- Don't forget to help stopping the braindumps, use of which reduces value of your certifications. Sign the petition at http://www.stopbraindumps.com/Blogs and organic groups at http://www.ccie.net
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