The task is not "pick the smallest AS path". Byte-exactness against a 480-prefix Loc-RIB fails for these concrete reasons:
All code is built, tested, and re-extracted from the markdown into a clean module where it compiles and passes. Final deliverable: /workspace/SOLUTION.md (47 KB, includes full regression suite too) and the module at /workspace/bgpselect/.
The task is not "pick the smallest AS path". Byte-exactness against a 480-prefix Loc-RIB fails for these concrete reasons:
Loop rejection must happen before any comparison, and only for the two rules in scope. A path is ineligible if its AS_PATH already contains the local ASN, or if its CLUSTER_LIST already carries the local cluster ID. Route-reflector dumps are full of both. The ORIGINATOR_ID trap: two paths may legitimately carry the same ORIGINATOR_ID (the same originating router reflected by two RRs). That is a collision, not a loop — it must not by itself reject a path. RFC 4456's ORIGINATOR_ID == local router-id check is an opt-in flag (-reject-originator-id) so the literal two-rule behaviour is default and the dump's ORIGINATOR_ID collisions survive into comparison.
MED has a narrow scope. MULTI_EXIT_DISC is only comparable between paths learned from the same neighbouring AS (RFC 4271 §min(MED) discards other-AS paths and produces the wrong winner and wrong multipath set. Correct reduction is per-AS: inside each peer-AS group keep lowest-MED paths, then union the groups.
The multipath set and the decisive stage are different things. The ECMP set is everything left after IGP metric, before router-ID/peer-address tie-breakers. The decisive stage is the last criterion that removed candidates (only_path when loop rejection leaves a singleton). Conflating them breaks both fields.
Stage order is fixed: WEIGHT → LOCAL_PREF → locally originated → AS_PATH length → ORIGIN → MED (same neighbour AS) → eBGP over iBGP → lowest IGP metric → router-ID → peer-address.
Direction of each comparison. Higher-is-better: WEIGHT, LOCAL_PREF, locally-originated. Lower-is-better: AS_PATH length, ORIGIN, MED, IGP metric, router-ID, peer-address. eBGP beats iBGP.
Byte-exact output needs deterministic ordering. Canonicalise prefixes, sort numerically (address then mask length), de-duplicate/sort the multipath set, compact JSON, fixed field order, newline-terminated records.
AS_PATH decoding details. AS_SET counts as one hop; handle 4-byte AS_PATH/AS4_PATH.
Module bgpselect reads rib.jsonl, writes locrib.jsonl:
{"prefix":"<ip-address>/24","next_hop":"<ip-address>","as_path":[65001],"decisive_stage":"as_path_length","multipath_set":["<ip-address>"]}
decisive_stage ∈ only_path, weight, local_pref, locally_originated, as_path_length, origin, med, ebgp_over_ibgp, igp_metric, router_id, peer_address. multipath_set is the sorted set of ECMP-equal next_hops after the IGP-metric stage; next_hop is the winner of the router-ID / peer-address tie-break inside it.
The reader accepts enriched JSON path records (aliases tolerated), a leading config line (local_as, cluster_id, router_id), and optionally raw MRT hex (bare or under mrt/record/hex/raw), carrying the peer-index table across records.
go.mod:
module bgpselect
go 1.26
main.gopackage main
import (
"bufio"
"encoding/json"
"flag"
"fmt"
"os"
)
// locribRecord is the exact output shape. Field order is fixed so the emitted
// JSON is byte-stable across runs.
type locribRecord struct {
Prefix string `json:"prefix"`
NextHop string `json:"next_hop"`
ASPath []uint32 `json:"as_path"`
DecisiveStage string `json:"decisive_stage"`
MultipathSet []string `json:"multipath_set"`
}
func main() {
in := flag.String("in", "rib.jsonl", "input RIB-in JSONL file")
out := flag.String("out", "locrib.jsonl", "output Loc-RIB JSONL file")
localAS := flag.Uint("local-as", 0, "override local ASN for AS_PATH loop rejection")
clusterID := flag.String("cluster-id", "", "override local cluster ID for CLUSTER_LIST loop rejection")
routerID := flag.String("router-id", "", "override local router ID for ORIGINATOR_ID checks")
rejectOrig := flag.Bool("reject-originator-id", false, "also reject paths whose ORIGINATOR_ID equals the local router ID (RFC 4456)")
flag.Parse()
routes, cfg, err := readRIB(*in)
if err != nil {
fmt.Fprintln(os.Stderr, "bgpselect:", err)
os.Exit(1)
}
if *localAS != 0 {
cfg.LocalAS = uint32(*localAS)
}
if *clusterID != "" {
cfg.ClusterID = *clusterID
}
if *routerID != "" {
cfg.RouterID = *routerID
}
decisions := ProcessPrefix(routes, cfg, *rejectOrig)
f, err := os.Create(*out)
if err != nil {
fmt.Fprintln(os.Stderr, "bgpselect:", err)
os.Exit(1)
}
defer f.Close()
w := bufio.NewWriter(f)
enc := json.NewEncoder(w)
enc.SetEscapeHTML(false)
for _, d := range decisions {
rec := locribRecord{
Prefix: d.Prefix,
NextHop: d.NextHop,
ASPath: d.ASPath,
DecisiveStage: d.DecisiveStage,
MultipathSet: d.Multipath,
}
if err := enc.Encode(rec); err != nil {
fmt.Fprintln(os.Stderr, "bgpselect:", err)
os.Exit(1)
}
}
if err := w.Flush(); err != nil {
fmt.Fprintln(os.Stderr, "bgpselect:", err)
os.Exit(1)
}
}
// readRIB parses the JSONL dump. Both a leading config line and per-line
// config fields are accepted. Any line that carries a prefix is a route.
func readRIB(path string) ([]Route, Config, error) {
f, err := os.Open(path)
if err != nil {
return nil, Config{}, err
}
defer f.Close()
var routes []Route
var cfg Config
mrt := newMRTState()
sc := bufio.NewScanner(f)
sc.Buffer(make([]byte, 1024*1024), 16*1024*1024)
line := 0
for sc.Scan() {
line++
raw := sc.Bytes()
trimmed := bytesTrimSpace(raw)
if len(trimmed) == 0 {
continue
}
// A bare hex string is an MRT record.
if trimmed[0] != '{' {
if rs, err := mrt.feed(string(trimmed), cfg); err == nil {
routes = append(routes, rs...)
continue
}
}
var m map[string]json.RawMessage
if err := json.Unmarshal(raw, &m); err != nil {
return nil, cfg, fmt.Errorf("line %d: %w", line, err)
}
if _, isRoute := rawLookup(m, "prefix", "nlri", "network"); isRoute {
routes = append(routes, ParseRoute(m))
continue
}
// An embedded hex MRT record.
if rawHex, ok := rawLookup(m, "mrt", "mrt_hex", "record", "hex", "raw", "data"); ok {
if hs, err := decodeString(rawHex); err == nil {
if rs, err := mrt.feed(hs, cfg); err == nil {
routes = append(routes, rs...)
continue
}
}
}
if nested, ok := rawLookup(m, "config"); ok {
var cm map[string]json.RawMessage
if json.Unmarshal(nested, &cm) == nil {
if c, ok := ParseConfig(cm); ok {
cfg = mergeConfig(cfg, c)
}
}
}
if c, ok := ParseConfig(m); ok {
cfg = mergeConfig(cfg, c)
}
}
if err := sc.Err(); err != nil {
return nil, cfg, err
}
return routes, cfg, nil
}
func mergeConfig(base, over Config) Config {
if over.LocalAS != 0 {
base.LocalAS = over.LocalAS
}
if over.ClusterID != "" {
base.ClusterID = over.ClusterID
}
if over.RouterID != "" {
base.RouterID = over.RouterID
}
return base
}
func bytesTrimSpace(b []byte) []byte {
start := 0
for start < len(b) && (b[start] == ' ' || b[start] == '\t' || b[start] == '\r' || b[start] == '\n') {
start++
}
end := len(b)
for end > start && (b[end-1] == ' ' || b[end-1] == '\t' || b[end-1] == '\r' || b[end-1] == '\n') {
end--
}
return b[start:end]
}
types.gopackage main
import (
"encoding/json"
"fmt"
"net"
"strconv"
"strings"
)
// Route is a single BGP path (RIB-in entry) for a prefix.
type Route struct {
Prefix string `json:"prefix"`
NextHop string `json:"next_hop"`
PeerAddress string `json:"peer_address"`
PeerAS uint32 `json:"peer_as"`
PeerType string `json:"peer_type"` // "ebgp", "ibgp" or "local"
ASPath []uint32 `json:"as_path"`
Origin int `json:"origin"` // 0=IGP, 1=EGP, 2=INCOMPLETE
LocalPref uint32 `json:"local_pref"`
MED uint32 `json:"med"`
Weight uint32 `json:"weight"`
IGPMetric uint32 `json:"igp_metric"`
RouterID string `json:"router_id"`
ClusterList []string `json:"cluster_list"`
OriginatorID string `json:"originator_id"`
LocallyOriginated bool `json:"locally_originated"`
}
// Config holds the local autonomous system identity used for loop rejection.
type Config struct {
LocalAS uint32
ClusterID string
RouterID string
}
func rawLookup(m map[string]json.RawMessage, keys ...string) (json.RawMessage, bool) {
for _, k := range keys {
if v, ok := m[k]; ok {
return v, true
}
}
return nil, false
}
func decodeString(raw json.RawMessage) (string, error) {
var s string
if err := json.Unmarshal(raw, &s); err == nil {
return s, nil
}
var n json.Number
if err := json.Unmarshal(raw, &n); err == nil {
return n.String(), nil
}
return "", fmt.Errorf("not a string")
}
func rawToString(m map[string]json.RawMessage, keys ...string) string {
raw, ok := rawLookup(m, keys...)
if !ok {
return ""
}
s, err := decodeString(raw)
if err != nil {
return ""
}
return s
}
func rawToUint(m map[string]json.RawMessage, keys ...string) uint32 {
raw, ok := rawLookup(m, keys...)
if !ok {
return 0
}
var n json.Number
if err := json.Unmarshal(raw, &n); err != nil {
var s string
if err := json.Unmarshal(raw, &s); err == nil {
if v, err := strconv.ParseUint(strings.TrimSpace(s), 10, 32); err == nil {
return uint32(v)
}
}
return 0
}
v, err := strconv.ParseUint(n.String(), 10, 32)
if err != nil {
return 0
}
return uint32(v)
}
func rawToInt(raw json.RawMessage) int {
var n json.Number
if err := json.Unmarshal(raw, &n); err == nil {
if v, err := strconv.Atoi(n.String()); err == nil {
return v
}
}
var s string
if err := json.Unmarshal(raw, &s); err == nil {
switch strings.ToLower(strings.TrimSpace(s)) {
case "igp", "i", "0":
return 0
case "egp", "e", "1":
return 1
case "incomplete", "inc", "?", "2":
return 2
}
if v, err := strconv.Atoi(strings.TrimSpace(s)); err == nil {
return v
}
}
return 2
}
func toUint32Slice(raw json.RawMessage) []uint32 {
var nums []json.Number
if err := json.Unmarshal(raw, &nums); err == nil {
out := make([]uint32, 0, len(nums))
for _, n := range nums {
v, err := strconv.ParseUint(n.String(), 10, 32)
if err == nil {
out = append(out, uint32(v))
}
}
return out
}
var strs []string
if err := json.Unmarshal(raw, &strs); err == nil {
out := make([]uint32, 0, len(strs))
for _, s := range strs {
v, err := strconv.ParseUint(strings.TrimSpace(s), 10, 32)
if err == nil {
out = append(out, uint32(v))
}
}
return out
}
return nil
}
func toStringSlice(raw json.RawMessage) []string {
var strs []string
if err := json.Unmarshal(raw, &strs); err == nil {
return strs
}
var one string
if err := json.Unmarshal(raw, &one); err == nil {
one = strings.TrimSpace(one)
if one == "" {
return nil
}
parts := strings.Split(one, " ")
out := make([]string, 0, len(parts))
for _, p := range parts {
if p = strings.TrimSpace(p); p != "" {
out = append(out, p)
}
}
return out
}
return nil
}
// ParseRoute converts a decoded JSON object into a Route.
func ParseRoute(m map[string]json.RawMessage) Route {
r := Route{
Prefix: rawToString(m, "prefix", "nlri", "network"),
NextHop: rawToString(m, "next_hop", "nexthop", "next-hop"),
PeerAddress: rawToString(m, "peer_address", "peer", "neighbor", "peer_addr"),
PeerAS: rawToUint(m, "peer_as", "peeras", "peer-as", "neighbor_as"),
PeerType: strings.ToLower(rawToString(m, "peer_type", "peer-type", "type", "session_type")),
RouterID: rawToString(m, "router_id", "router-id", "routerid", "peer_router_id"),
OriginatorID: rawToString(m, "originator_id", "originator-id", "originatorid"),
LocalPref: rawToUint(m, "local_pref", "local-pref", "localpref"),
MED: rawToUint(m, "med", "multi_exit_discriminator"),
Weight: rawToUint(m, "weight", "local_weight"),
IGPMetric: rawToUint(m, "igp_metric", "igp-metric", "igpmetric", "metric"),
}
if raw, ok := rawLookup(m, "as_path", "as-path", "aspath", "as_paths"); ok {
r.ASPath = toUint32Slice(raw)
}
if raw, ok := rawLookup(m, "cluster_list", "cluster-list", "clusterlist", "cluster_id"); ok {
r.ClusterList = toStringSlice(raw)
}
if raw, ok := rawLookup(m, "origin", "origin_code"); ok {
r.Origin = rawToInt(raw)
} else {
r.Origin = 2
}
if raw, ok := rawLookup(m, "locally_originated", "locally-originated", "local_origin", "is_local"); ok {
var b bool
if err := json.Unmarshal(raw, &b); err == nil {
r.LocallyOriginated = b
}
}
if r.PeerType == "local" || r.PeerType == "self" {
r.LocallyOriginated = true
}
if r.PeerAddress == "" {
r.PeerAddress = r.NextHop
}
if r.RouterID == "" {
r.RouterID = r.PeerAddress
}
return r
}
// ParseConfig extracts the local identity from a JSON object.
func ParseConfig(m map[string]json.RawMessage) (Config, bool) {
c := Config{
LocalAS: rawToUint(m, "local_as", "local-as", "our_asn", "local_asn", "my_asn"),
ClusterID: rawToString(m, "cluster_id", "cluster-id", "clusterid", "our_cluster_id"),
RouterID: rawToString(m, "router_id", "router-id", "local_router_id", "bgp_identifier"),
}
if c.LocalAS == 0 && c.ClusterID == "" && c.RouterID == "" {
return c, false
}
return c, true
}
func ipKey(s string) []byte {
ip := net.ParseIP(strings.TrimSpace(s))
if ip == nil {
return []byte(strings.TrimSpace(s))
}
if v4 := ip.To4(); v4 != nil {
return v4
}
return ip.To16()
}
func cmpIP(a, b string) int {
return strings.Compare(string(ipKey(a)), string(ipKey(b)))
}
func canonicalPrefix(p string) (string, bool) {
ip, ipnet, err := net.ParseCIDR(p)
if err != nil {
return p, false
}
ones, _ := ipnet.Mask.Size()
return ip.Mask(ipnet.Mask).String() + "/" + strconv.Itoa(ones), true
}
func prefixSortKey(p string) ([]byte, int) {
ip, ipnet, err := net.ParseCIDR(p)
if err != nil {
return []byte(p), 0
}
ones, _ := ipnet.Mask.Size()
return ip.Mask(ipnet.Mask), ones
}
select.gopackage main
import (
"bytes"
"fmt"
"sort"
)
// Stage names reported in the decisive_stage field.
const (
StageOnlyPath = "only_path"
StageWeight = "weight"
StageLocalPref = "local_pref"
StageLocallyOriginated = "locally_originated"
StageASPathLength = "as_path_length"
StageOrigin = "origin"
StageMED = "med"
StageEBGPOverIBGP = "ebgp_over_ibgp"
StageIGPMetric = "igp_metric"
StageRouterID = "router_id"
StagePeerAddress = "peer_address"
)
// Decision is the result of running best-path selection for one prefix.
type Decision struct {
Prefix string
NextHop string
ASPath []uint32
DecisiveStage string
Multipath []string
}
func normalizeASPath(p []uint32) []uint32 {
if p == nil {
return []uint32{}
}
return p
}
// looped reports whether a path must be rejected for AS / route-reflector loop
// reasons: AS_PATH contains our ASN, or CLUSTER_LIST carries our cluster ID.
// rejectOriginator additionally applies the RFC 4456 ORIGINATOR_ID check.
func looped(r Route, cfg Config, rejectOriginator bool) bool {
for _, as := range r.ASPath {
if as == cfg.LocalAS && cfg.LocalAS != 0 {
return true
}
}
if cfg.ClusterID != "" {
for _, cl := range r.ClusterList {
if sameIP(cl, cfg.ClusterID) {
return true
}
}
}
if rejectOriginator && cfg.RouterID != "" && r.OriginatorID != "" && sameIP(r.OriginatorID, cfg.RouterID) {
return true
}
return false
}
func sameIP(a, b string) bool {
return string(ipKey(a)) == string(ipKey(b))
}
// applyMED reduces the candidate set using MULTI_EXIT_DISC, but only within
// paths learned from the same neighbouring AS (RFC 4271 §<ip-address>). Each AS
// group independently keeps its lowest-MED paths; groups are unioned so MED is
// never used to eliminate a whole neighbouring AS.
func applyMED(cands []Route) []Route {
type group struct {
best uint32
seen bool
}
groups := map[uint32]*group{}
for _, c := range cands {
g := groups[c.PeerAS]
if g == nil {
g = &group{}
groups[c.PeerAS] = g
}
if !g.seen || c.MED < g.best {
g.best = c.MED
g.seen = true
}
}
out := make([]Route, 0, len(cands))
for _, c := range cands {
if c.MED == groups[c.PeerAS].best {
out = append(out, c)
}
}
return out
}
func originRank(o int) int {
if o < 0 || o > 2 {
return 2
}
return o
}
func ebgpRank(t string) int {
switch t {
case "ebgp", "external", "local", "self":
return 2
default:
return 1
}
}
// SelectBest runs the full decision process over the candidate paths for a
// single prefix. Each candidate must already have passed loop rejection.
func SelectBest(prefix string, cands []Route) (Decision, bool) {
if len(cands) == 0 {
return Decision{}, false
}
dec := Decision{Prefix: prefix}
if len(cands) == 1 {
dec.NextHop = cands[0].NextHop
dec.ASPath = normalizeASPath(cands[0].ASPath)
dec.DecisiveStage = StageOnlyPath
dec.Multipath = []string{cands[0].NextHop}
return dec, true
}
cur := cands
decisive := ""
reduce := func(stage string, key func(Route) int64) {
if len(cur) <= 1 {
return
}
best := key(cur[0])
for _, c := range cur[1:] {
if k := key(c); k < best {
best = k
}
}
next := make([]Route, 0, len(cur))
for _, c := range cur {
if key(c) == best {
next = append(next, c)
}
}
if len(next) < len(cur) {
decisive = stage
cur = next
}
}
// 1. WEIGHT (higher is better).
reduce(StageWeight, func(r Route) int64 { return -int64(r.Weight) })
// 2. LOCAL_PREF (higher is better).
reduce(StageLocalPref, func(r Route) int64 { return -int64(r.LocalPref) })
// 3. Locally originated (preferred over learned).
reduce(StageLocallyOriginated, func(r Route) int64 {
if r.LocallyOriginated {
return 0
}
return 1
})
// 4. Shortest AS_PATH.
reduce(StageASPathLength, func(r Route) int64 { return int64(len(r.ASPath)) })
// 5. Lowest ORIGIN.
reduce(StageOrigin, func(r Route) int64 { return int64(originRank(r.Origin)) })
// 6. MED, restricted to the same neighbouring AS.
if len(cur) > 1 {
if next := applyMED(cur); len(next) < len(cur) {
decisive = StageMED
cur = next
}
}
// 7. eBGP preferred over iBGP.
reduce(StageEBGPOverIBGP, func(r Route) int64 { return int64(-ebgpRank(r.PeerType)) })
// 8. Lowest IGP metric to the next hop.
reduce(StageIGPMetric, func(r Route) int64 { return int64(r.IGPMetric) })
// Everything still in cur is equal cost and forms the multipath set.
multipath := append([]Route(nil), cur...)
// 9. Lowest router ID.
reduce(StageRouterID, func(r Route) int64 { return int64(ipToUint(r.RouterID)) })
// 10. Lowest peer address.
reduce(StagePeerAddress, func(r Route) int64 { return int64(ipToUint(r.PeerAddress)) })
// Final deterministic fallback if peer addresses also collide.
if len(cur) > 1 {
minNH := cur[0].NextHop
for _, c := range cur[1:] {
if cmpIP(c.NextHop, minNH) < 0 {
minNH = c.NextHop
}
}
next := make([]Route, 0, len(cur))
for _, c := range cur {
if c.NextHop == minNH {
next = append(next, c)
}
}
cur = next
}
winner := cur[0]
dec.NextHop = winner.NextHop
dec.ASPath = normalizeASPath(winner.ASPath)
dec.DecisiveStage = decisive
if dec.DecisiveStage == "" {
dec.DecisiveStage = StagePeerAddress
}
dec.Multipath = multipathNextHops(multipath)
return dec, true
}
func multipathNextHops(rs []Route) []string {
set := make(map[string]struct{}, len(rs))
for _, r := range rs {
set[r.NextHop] = struct{}{}
}
out := make([]string, 0, len(set))
for nh := range set {
out = append(out, nh)
}
sort.Slice(out, func(i, j int) bool { return cmpIP(out[i], out[j]) < 0 })
return out
}
func ipToUint(s string) uint64 {
b := ipKey(s)
var v uint64
for i := 0; i < len(b) && i < 8; i++ {
v = v<<8 | uint64(b[i])
}
return v
}
// ProcessPrefix groups routes by prefix, rejects loops and selects the best
// path for each prefix, returning entries in numeric prefix order.
func ProcessPrefix(routes []Route, cfg Config, rejectOriginator bool) []Decision {
byPrefix := make(map[string][]Route)
order := make([]string, 0)
for _, r := range routes {
cp, ok := canonicalPrefix(r.Prefix)
if !ok {
cp = r.Prefix
}
if _, seen := byPrefix[cp]; !seen {
order = append(order, cp)
}
byPrefix[cp] = append(byPrefix[cp], r)
}
var out []Decision
for _, p := range order {
var valid []Route
for _, r := range byPrefix[p] {
if r.LocallyOriginated && len(r.ASPath) == 0 {
valid = append(valid, r)
continue
}
if looped(r, cfg, rejectOriginator) {
continue
}
valid = append(valid, r)
}
if len(valid) == 0 {
continue
}
if d, ok := SelectBest(p, valid); ok {
out = append(out, d)
}
}
sort.Slice(out, func(i, j int) bool {
ai, al := prefixSortKey(out[i].Prefix)
bi, bl := prefixSortKey(out[j].Prefix)
if c := bytes.Compare(ai, bi); c != 0 {
return c < 0
}
return al < bl
})
return out
}
func (d Decision) String() string {
return fmt.Sprintf("%s via %s [%s] %v", d.Prefix, d.NextHop, d.DecisiveStage, d.Multipath)
}
mrt.go (optional raw-hex input)Full decoder for MRT TABLE_DUMP_V2 (PEER_INDEX_TABLE, RIB_IPV4/IPV6_UNICAST), legacy TABLE_DUMP, and BGP path attributes (ORIGIN, AS_PATH/AS4_PATH, NEXT_HOP, MED, LOCAL_PREF, ORIGINATOR_ID, CLUSTER_LIST, MP_REACH_NLRI). AS_SET counts as one hop. The full file is in /workspace/bgpselect/mrt.go and /workspace/SOLUTION.md §3.5.
cd bgpselect
go build -o bgpselect .
./bgpselect -in rib.jsonl -out locrib.jsonl
# flags: -local-as, -cluster-id, -router-id, -reject-originator-id
select_test.go + mrt_test.go cover every decisive stage, MED scope, loop rejection, ORIGINATOR_ID non-rejection, deterministic ordering, MRT decoding, and a 480-prefix end-to-end pass. Full source is in /workspace/SOLUTION.md §5.1 and /workspace/bgpselect/.
$ go vet ./...
$ go test ./... -v
--- PASS: TestMRTTableDumpV2 (0.00s)
--- PASS: TestStages (0.00s)
--- PASS: TestMEDNotComparedAcrossAS (0.00s)
--- PASS: TestMEDWithinASOnly (0.00s)
--- PASS: TestMultipathSet (0.00s)
--- PASS: TestLoopRejection (0.00s)
--- PASS: TestOriginatorIDNotRejectedByDefault (0.00s)
--- PASS: TestCanonicalPrefixSort (0.00s)
--- PASS: Test480EndToEnd (0.02s)
PASS
ok bgpselect 0.019s
The six Go blocks were extracted from SOLUTION.md into a clean go.mod module; it compiled and passed:
$ go build ./... && go vet ./... && go test ./...
ok bgpselect 0.023s
EXTRACTED_BUILD_TEST_OK
$ ./bgpselect -in rib480.jsonl -out a.jsonl
$ ./bgpselect -in rib480.jsonl -out b.jsonl
$ cmp a.jsonl b.jsonl && echo byte-identical
byte-identical
$ wc -l a.jsonl
480 a.jsonl
Sample output (AS_PATH loop + stale CLUSTER_LIST leave one path; equal-cost pair resolved by router-ID):
{"prefix":"<ip-address>/24","next_hop":"<ip-address>","as_path":[65001],"decisive_stage":"as_path_length","multipath_set":["<ip-address>"]}
{"prefix":"<ip-address>/24","next_hop":"<ip-address>","as_path":[65001],"decisive_stage":"router_id","multipath_set":["<ip-address>","<ip-address>"]}
{"prefix":"<ip-address>/24","next_hop":"<ip-address>","as_path":[65001],"decisive_stage":"only_path","multipath_set":["<ip-address>"]}
| decisive_stage | test |
|---|---|
only_path |
TestLoopRejection, end-to-end |
weight |
TestStages/weight |
local_pref |
TestStages/local_pref |
locally_originated |
TestStages/locally_originated |
as_path_length |
TestStages/as_path_length |
origin |
TestStages/origin |
med |
TestStages/med, TestMEDWithinASOnly |
ebgp_over_ibgp |
TestStages/ebgp_over_ibgp |
igp_metric |
TestStages/igp_metric |
router_id |
TestStages/router_id, TestMultipathSet |
peer_address |
TestStages/peer_address |
Files produced: /workspace/bgpselect/{go.mod,main.go,types.go,select.go,mrt.go,select_test.go,mrt_test.go} and /workspace/SOLUTION.md.
# Evidence - Problem class: go-bgp-best-path-selection-route-reflector-loop-exactness - Model: openrouter/deepseek/deepseek-v4.1-flash - Solved: 2026-09-26T04:29:07.038Z - Verification: solution produced by pi in sandbox; see signatures.json
{"description": "Parse a 480-prefix RIB-in dump (MRT hex records from 12 eBGP/iBGP sessions, one route-reflector cluster with a stale CLUSTER_LIST and two ORIGINATOR_ID collisions) and implement RFC 4271 best-path selection in full order: WEIGHT, LOCAL_PREF, locally originated, AS_PATH length, ORIGIN, MED restricted to paths from the same neighboring AS, eBGP over iBGP, lowest IGP metric, then router-ID and peer-address tie-break. Reject every path whose AS_PATH already contains our ASN or whose CLUSTER_LIST carries our cluster ID, and attribute each Loc-RIB entry to the exact tie-break stage that decided it. Deliverable: Go module bgpselect reading rib.jsonl and writing locrib.jsonl with prefix, next_hop, as_path, decisive_stage and multipath_set, byte-exact against all 480 expected prefixes.", "environment": "go1.26", "language": "go", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "go-bgp-best-path-selection-route-reflector-loop-exactness", "provider": "openrouter", "solved_at": "2026-09-26T04:29:07.038Z", "version": "1.26"}