Vodafone allows customers to control certain traffic flows off-net with the implementation of BGP community attribute values that prepend route/prefix paths with additional AS hops. These community attribute values, which the customer applies, affects the way Vodafone peers choose the degree of preference of a given prefix/route, because the number of AS hops within the route-path has been lengthened.
The format for the second component of customer route community number (after 1273:) is set at five digits. This fixed length allows regular expressions to be used in applying a defined number of prepends to a given route/prefix path. This format is 1273:3PPPN, where the fields are coded in the following way. (Note: The first digit of the second component is always "3" then followed by variables of the "PPP" and "N" variables which are defined in the following tables.)
The "PPP" variable cross references off-net connections of Vodafone (please note that some of these are v6 only), defined in the following tables. (Note, this will always be a three digit value.)
The "N" variable cross references the number of prepends, defined in the following table.
Do not announce to selected peer
Prepend 1x to selected peer
Prepend 2x to selected peer
Prepend 3x to selected peer
Announce to this peer only (also announces to customers)
1273:32000 - Do not announce to Verizon Europe (AS702)
1273:31752 - Prepend twice to Reach (AS4637)
1273:39963 - Prepend three times to Level 3 Upstream connection (AS3356)
Please note that mixing a 'prepend to IXP' or 'prepend to region' community with a 'prepend to specific peer' or global community may not have the intended effect. Prepending once to LINX and once to BT will lead to the route being prepended once to BT at LINX, whereas prepending an unequal number of times to an IXP and a peer at that IXP will lead to the sum of the prepends being added (e.g. prepending once to LINX and twice to BT will lead to three prepends being sent to BT at LINX). For this reason it is not recommended to mix specific and general prepend communities on the same routes.
Vodafone Blackhole Community Attribute Values (1273:666)
For customers that have a host or block under a DDoS, the affected host/block can be advertised to AS1273 with community string 1273:666. This will cause all traffic to that host/block to be black-holed at the core of the AS1273 network. After advertising the prefix with 1273:666, the customer may open a ticket to request further assistance with their Vodafone Customer Front Office. Once the attack has been mitigated, the customer will be responsible for removing the prefix from being advertised. Vodafone will not be held responsible for customers who errantly advertise prefixes with the Blackhole community string.
Vodafone local preference alteration communities
The local-preference hierarchy within Vodafone AS1273 is as follows
Customers (BGP and injected static)
Backup customer connections
Last resort customer connections
The following communities can be sent to influence the local-preference of a customer route
Sets local preference value within AS1273 to 90
Sets local preference value within AS1273 to 80
Sets local preference value within AS1273 to 70
Prevents this route from being announce to any AS1273 EBGP peer
Prevents this route from being announced to any AS1273 EBGP or IBGP peer