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Ip As-Path ---explain

Can someone explain this word by word please:
IP AS-PATH Access-list 10 permit ^$
Route map SetMed
Match AS-PATH 10
Set Metric 1000

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jskfan
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jskfan
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1 Solution
 
Garry GlendownConsulting and Network/Security SpecialistCommented:
The AS path access list defines a filter, which matches any prefixes that do not have any AS attached (i.e. internally sourced inside your network). This is then used to set the metric to these addresses to a value of 1000, which probably means on a BGP level you'll most likely prefer routing towards those addresses via other links, if any such exist. Not sure why this would be done globally, but there may be other limitations in place of course ...
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jskfanAuthor Commented:
1- I mean , do you have to create an Access-list 10 ?
2- is there another IP command for other BGP attribute, I mean instead of IP AS-PATH, something else ; IP WEIGHT, or IP Local-Preference.etc....
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Garry GlendownConsulting and Network/Security SpecialistCommented:
The route map needs the access list (could also be anextended/named access list) to use as a basis for the decission whether the following statements are executed.

Yes there are other things you can change, like prepends, local preference etc... just use the "?" after the "set" command to see the available options. (posting mobile or I'd copy a list of available options)
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jskfanAuthor Commented:
Ok So,
Access-list 10  must be created before or after this command :
IP AS-PATH Access-list 10 permit ^$
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Garry GlendownConsulting and Network/Security SpecialistCommented:
Slight misunderstanding - this is an AS-Path access list, it has nothing to do with a regular "access list" as in "ip access-list" or "access-list 10 permit ...", and is configured by the above syntax ... no additional things have to be configured for it... (please ignore the "extended/named" access list comment of mine above ... I must have been sleeping ;) )
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jskfanAuthor Commented:
Clear Garry-G now.

Thanks
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jskfanAuthor Commented:
Excellent explanation
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