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bgpd: compare aigp after local route check in bgp_path_info_cmp() #17242

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Oct 29, 2024
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bgpd: compare aigp after local route check in bgp_path_info_cmp() #17242

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55 changes: 26 additions & 29 deletions bgpd/bgp_route.c
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Original file line number Diff line number Diff line change
Expand Up @@ -923,7 +923,32 @@ static int bgp_path_info_cmp(struct bgp *bgp, struct bgp_path_info *new,
}
}

/* Tie-breaker - AIGP (Metric TLV) attribute */
/* 3. Local route check. We prefer:
* - BGP_ROUTE_STATIC
* - BGP_ROUTE_AGGREGATE
* - BGP_ROUTE_REDISTRIBUTE
*/
new_origin = !(new->sub_type == BGP_ROUTE_NORMAL || new->sub_type == BGP_ROUTE_IMPORTED);
exist_origin = !(exist->sub_type == BGP_ROUTE_NORMAL ||
exist->sub_type == BGP_ROUTE_IMPORTED);

if (new_origin && !exist_origin) {
*reason = bgp_path_selection_local_route;
if (debug)
zlog_debug("%s: %s wins over %s due to preferred BGP_ROUTE type", pfx_buf,
new_buf, exist_buf);
return 1;
}

if (!new_origin && exist_origin) {
*reason = bgp_path_selection_local_route;
if (debug)
zlog_debug("%s: %s loses to %s due to preferred BGP_ROUTE type", pfx_buf,
new_buf, exist_buf);
return 0;
}

/* 3.5. Tie-breaker - AIGP (Metric TLV) attribute */
if (CHECK_FLAG(newattr->flag, ATTR_FLAG_BIT(BGP_ATTR_AIGP)) &&
CHECK_FLAG(existattr->flag, ATTR_FLAG_BIT(BGP_ATTR_AIGP)) &&
CHECK_FLAG(bgp->flags, BGP_FLAG_COMPARE_AIGP)) {
Expand Down Expand Up @@ -953,34 +978,6 @@ static int bgp_path_info_cmp(struct bgp *bgp, struct bgp_path_info *new,
}
}

/* 3. Local route check. We prefer:
* - BGP_ROUTE_STATIC
* - BGP_ROUTE_AGGREGATE
* - BGP_ROUTE_REDISTRIBUTE
*/
new_origin = !(new->sub_type == BGP_ROUTE_NORMAL ||
new->sub_type == BGP_ROUTE_IMPORTED);
exist_origin = !(exist->sub_type == BGP_ROUTE_NORMAL ||
exist->sub_type == BGP_ROUTE_IMPORTED);

if (new_origin && !exist_origin) {
*reason = bgp_path_selection_local_route;
if (debug)
zlog_debug(
"%s: %s wins over %s due to preferred BGP_ROUTE type",
pfx_buf, new_buf, exist_buf);
return 1;
}

if (!new_origin && exist_origin) {
*reason = bgp_path_selection_local_route;
if (debug)
zlog_debug(
"%s: %s loses to %s due to preferred BGP_ROUTE type",
pfx_buf, new_buf, exist_buf);
return 0;
}

/* Here if these are imported routes then get ultimate pi for
* path compare.
*/
Expand Down
8 changes: 4 additions & 4 deletions doc/user/bgp.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -148,16 +148,16 @@ bottom until one of the factors can be used.

Prefer higher local preference routes to lower.

3. **Local route check**

Prefer local routes (statics, aggregates, redistributed) to received routes.

If ``bgp bestpath aigp`` is enabled, and both paths that are compared have
AIGP attribute, BGP uses AIGP tie-breaking unless both of the paths have the
AIGP metric attribute. This means that the AIGP attribute is not evaluated
during the best path selection process between two paths when one path does
not have the AIGP attribute.

3. **Local route check**

Prefer local routes (statics, aggregates, redistributed) to received routes.

4. **AS path length check**

Prefer shortest hop-count AS_PATHs.
Expand Down
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