Hi
I- Understood that it is possible to run BGP (say eBGP) to advertise plain IP4 and IP4+lable
(MP-BGP RFC 2858 + RFC 3107 ) simultaneusly .
Say we have such BGP session betyween R1 and R2 .
(R1 and R2 support MP-BGP for AFI =1 and SAFI=4 and also run the default IPV4)
Could R1 advertise Neta (say 10.0.0.0/8) once as plain Ip4 and also as IP4+lable ?
IF yes :
1-Could it be done as "A" or "B" or both are valid
A- The plain neta is encoded in the NLRI filed of the update msg (normal as per RFC 1771).
The IP4+lable is encoded as per RFC 2858 +RFC 3107 .
B- The plain neta is encoded as per RFC 2858+RFC 3107 but the label is encoded
as 0x800000 to indicate it is not labeled .
The IP4+lable is encoded as per RFC 2858 +RFC 3107 .
2- Is it mandary that the plain IPv4 and IPV4+label have the same & equal attributes
(Origin , AS-PATH ..etc ) to adhere to the BGP rule that only the best path should
be advertised to a peer . OR they could have different value of attributes ?
3- In case the plain IPv4 and IPV4+label have the same equal attributes
(Origin , AS-PATH ..etc ) . what is the selection rule -tie bracking- used by R2 to select
one of this 2 path ?? or it is just up to R2 (may be with some config) to select one over the
other .
II- Reg RFC3107 Section 4 " Advertising Multiple Routes to a Destination"
1-Quote
A BGP speaker may maintain (and advertise to its peers) more than
one route to a given destination, as long as each such route has
its own label(s).
Unquote
Is this statement conflict with BGP rule that only the best path
need to be advertised ???
What are the advantages or specific application which call to send
multiple route to a given destination over BGP ??
2- Quote
The encoding described above allows a single BGP Update message to carry multiple routes, each with its own label(s).
Unquote
Guess here to avoid ambiguity is to rewrite it as :
"The encoding described above allows a single BGP Update
message to carry multiple routes TO A GIVEN DESTINATION ,
each with its own label(s)."
is the label value "0x80000" is valid value for label to indicate it is unlabeled NLRI ??
3- Quote
In the case where a BGP speaker advertises multiple routes to a
destination, if a route is withdrawn, and a label(s) is specified at
the time of withdrawal, only the corresponding route with the
corresponding label is withdrawn. If a route is withdrawn, and no
label is specified at the time of withdrawal, then only the
corresponding unlabeled route is withdrawn; the labeled routes are
left in place.
Unquote
What it mean " and no label is specified" ? is it mean that the label value is set to
0x800000 or it mean that the route was adverised as unlabelled using lable value
0x800000 but later withdeawn by normal IP4 (RFC 1171 withdraw route fileds) .
Thncks in advance .
Brgds