BGP-4

netverdict models BGP as a deterministic control-plane protocol for labs, change analysis, and policy reasoning. It is not a router image, but it does track the behaviours that usually matter in training and review scenarios: sessions, route advertisement, best-path selection, AS_PATH, LOCAL_PREF, MED, communities, route-maps, route reflection, confederations, and VPNv4.

Support level

Area	Level	What this means
IPv4 unicast BGP	Supported	eBGP / iBGP sessions, network statements, UPDATE propagation, Loc-RIB, Adj-RIB-style views.
Best-path selection	Supported	Deterministic subset of RFC 4271 path selection.
Policy	Supported	Prefix-lists, AS-path ACLs, community-lists, route-maps, inbound and outbound application.
Path attributes	Supported	AS_PATH, NEXT_HOP, ORIGIN, LOCAL_PREF, MED, communities.
Communities	Supported	Standard communities, exact community-list matching, expanded community-list regex matching.
Route reflection	Supported	route-reflector-client for iBGP reflection labs.
Peer-groups	Supported	Cisco-style and VyOS-style template inheritance.
Confederations	Supported	RFC 5065-style AS confederation identifier, peers, and AS_PATH handling.
Graceful restart	Supported	RFC 4724-style stale-route window is modelled.
Maximum-prefix	Supported	Prefix-limit teardown with notification-style behaviour.
MP-BGP VPNv4	Supported	VPNv4 AF for L3VPN scenarios with RD / RT / VRF import-export behaviour.
Timers	Partial	Keepalive / hold / connect retry are deterministic simulation timers. Update damping knobs are modelled where listed below.
Packet fidelity	Partial	BGP packets are represented for traces / PCAP inspection, but the simulator is not a byte-for-byte vendor TCP stack.

Standards coverage

Standard	Coverage	Notes
RFC 4271, BGP-4	Behaviour model	OPEN / UPDATE-style session behaviour, route exchange, AS_PATH loop prevention, and best-path selection subset.
RFC 4271 section 5.1.2	Supported	AS_PATH is tracked and used for loop prevention and path length comparison.
RFC 4271 section 5.1.3	Supported	NEXT_HOP is tracked and used for recursive reachability decisions.
RFC 4271 section 5.1.4	Supported	MED is modelled and compared between routes from the same neighbouring AS.
RFC 4271 section 5.1.5	Supported	LOCAL_PREF defaults to 100 and can be changed by route-map or default local-preference.
RFC 4271 section 9.1.2.2	Behaviour model	Best-path order is deterministic and documented below.
RFC 2385, TCP MD5	Behaviour model	neighbor ... password must match on both sides for a session to establish. Real TCP MD5 bytes are not computed.
RFC 1997, Communities	Supported	Standard communities are attached, matched, and propagated in policy scenarios.
RFC 4364, BGP/MPLS IP VPNs	Behaviour model	VPNv4 routes, route distinguishers, route-target import/export, and VRF route projection are modelled.
RFC 4456, Route Reflection	Supported	Route-reflector clients can receive reflected iBGP routes.
RFC 4724, Graceful Restart	Supported	Restart-time and stale-path timers are modelled.
RFC 5065, Confederations	Supported	Confederation identifier, peer sub-AS list, and confed AS_PATH treatment are modelled.
RFC 4486, BGP Cease Subcodes	Behaviour model	Maximum-prefix teardown uses the maximum-prefix cease behaviour at the model level.

Best-path order

netverdict compares BGP candidates in this order:

Step	Rule
1	Higher LOCAL_PREF wins.
2	Locally originated routes win over received routes.
3	Shorter AS_PATH wins. Confederation segments do not count toward length.
4	Lower ORIGIN wins: igp, then egp, then incomplete.
5	Lower MED wins when both routes came from the same neighbouring AS.
6	eBGP-learned routes beat iBGP-learned routes.
7	Lower IGP cost to NEXT_HOP wins when the engine has a resolver.
8	Older route wins.
9	Lower advertising router / neighbour address wins as stable final tie-break.

This is intentionally deterministic. Replaying the same topology with the same commands should produce the same best path.

Feature matrix

Feature	Status	Notes
router bgp <asn>	Supported	One BGP process per device.
bgp router-id <ip>	Supported	Explicit router ID; otherwise derived by runtime.
IPv4 unicast AF	Supported	Default working AF for classic BGP labs.
address-family ipv4	Supported	Includes VRF sub-mode for per-VRF neighbours.
address-family vpnv4	Supported	Used by L3VPN / MP-BGP scenarios.
network <prefix> mask <mask>	Supported	Locally originates IPv4 unicast or AF-specific routes.
eBGP neighbours	Supported	Remote-AS mismatch prevents establishment.
iBGP neighbours	Supported	Same-AS neighbours participate in iBGP behaviour.
neighbor ... activate	Supported	Top-level and AF-level activation.
neighbor ... update-source	Supported	Source-interface setting for loopback-style sessions.
neighbor ... next-hop-self	Supported	Rewrites NEXT_HOP for outbound advertisements.
neighbor ... route-reflector-client	Supported	Enables route reflection for iBGP client scenarios.
neighbor ... peer-group	Supported	Peer-group templates and binding.
neighbor ... description	Supported	Stored and emitted for operator-visible config fidelity.
neighbor ... shutdown	Supported	Forces the session down.
neighbor ... ebgp-multihop	Supported	Stores and applies multihop eBGP reachability intent.
neighbor ... password	Behaviour model	Matching password required on both sides; no real TCP-MD5 segment hashing.
neighbor ... fall-over bfd	Supported	BFD-down forces BGP idle.
neighbor ... maximum-prefix	Supported	Tears down the session when accepted prefixes exceed the configured limit.
neighbor ... soft-reconfiguration inbound	Supported	Stores inbound pre-policy routes for received-route inspection.
neighbor ... advertisement-interval	Supported	Coalesces UPDATE bursts to the peer.
neighbor ... as-origination-interval	Supported	Coalesces locally-originated UPDATEs.
neighbor ... send-community	Accepted	Communities are sent when present; the command is accepted for config fidelity.
Prefix-list policy	Supported	neighbor ... prefix-list NAME in / out.
Route-map policy	Supported	neighbor ... route-map NAME in / out.
AS-path access-list	Supported	Regex-like AS_PATH matching in route-maps.
Standard community-list	Supported	Exact community matching.
Expanded community-list	Supported	JavaScript-regex match against printed <asn>:<n> form.
set local-preference	Supported	Route-map action.
set as-path prepend	Supported	Route-map action.
set metric	Supported	MED route-map action.
set community	Supported	Supports replacement, additive, and none.
set ip next-hop	Supported	Route-map action.
set origin	Supported	Route-map action.
bgp default local-preference	Supported	Default LOCAL_PREF for local originated routes.
bgp graceful-restart	Supported	Restart and stale-path timers are modelled.
bgp confederation identifier	Supported	Public confederation AS.
bgp confederation peers	Supported	Member sub-AS list.
aggregate-address	Stored	Accepted and emitted. Current FIB programming does not yet originate the aggregate route.
Unnumbered BGP	Config model	Stored for FRR / VyOS-style import, but IPv4 runtime sessions need numbered peers today.
Add-path	Not modelled	Only the selected best path is installed / advertised for normal IPv4 unicast.
Route flap damping	Not modelled	Advertisement interval is supported; full damping penalty logic is not.
RPKI / origin validation	Not modelled	Planned as a later policy/compliance feature.

Vendor command matrix

Command	IOS-style	Junos-style	VyOS-style	Notes
router bgp 65001	Supported	n/a	n/a	Cisco-family process mode.
bgp router-id 1.1.1.1	Supported	Supported	Supported	Maps to canonical router ID.
neighbor 10.0.0.2 remote-as 65002	Supported	Supported	Supported	Core numbered neighbour form.
neighbor 10.0.0.2 update-source Loopback0	Supported	Supported	Supported	Source-interface intent.
neighbor 10.0.0.2 next-hop-self	Supported	Supported	Supported	Also available in AF form on some vendors.
neighbor 10.0.0.2 route-reflector-client	Supported	Supported	Supported	Used for iBGP reflection scenarios.
neighbor 10.0.0.2 description TEXT	Supported	Supported	Supported	Stored / emitted as metadata.
neighbor 10.0.0.2 shutdown	Supported	Supported	Supported	Administrative down.
neighbor 10.0.0.2 ebgp-multihop 4	Supported	Supported	Supported	Multihop eBGP intent.
neighbor 10.0.0.2 password SECRET	Supported	Partial	Supported	Behaviour model for TCP-MD5-style password match.
neighbor 10.0.0.2 fall-over bfd	Supported	Not yet	Partial	BFD integration exists in canonical model.
neighbor 10.0.0.2 maximum-prefix 100	Supported	Not yet	Partial	Prefix-limit session teardown.
neighbor 10.0.0.2 route-map RM in	Supported	Partial	Supported	Policy maps to canonical route-map references.
neighbor 10.0.0.2 prefix-list PL out	Supported	Partial	Supported	Prefix-list policy.
neighbor PEERS peer-group	Supported	n/a	Supported	Template / inheritance model.
neighbor 10.0.0.2 peer-group PEERS	Supported	n/a	Supported	Binding to template.
address-family ipv4	Supported	n/a	Supported	Cisco / VyOS syntax differs but maps to IPv4 unicast AF.
address-family ipv4 vrf BLUE	Supported	Partial	Partial	Per-VRF IPv4 BGP for L3VPN edge cases.
address-family vpnv4	Supported	Partial	Partial	MP-BGP VPNv4 scenarios.
network 192.0.2.0 mask 255.255.255.0	Supported	Supported	Supported	Locally originated route.
bgp default local-preference 200	Supported	Supported	Partial	Default local-pref for local originated routes.
bgp graceful-restart	Supported	Supported	Supported	Restart / stale-path timers where syntax is implemented.
bgp confederation identifier 65000	Supported	Partial	Supported	RFC 5065 model.
bgp confederation peers 65001 65002	Supported	Partial	Supported	Member sub-AS list.
aggregate-address 10.0.0.0 255.0.0.0	Stored	Not yet	Not yet	Accepted / emitted; aggregate route origination not yet active.
show ip bgp	Supported	Vendor-shaped view	Vendor-shaped view	Loc-RIB / best-path table.
show ip bgp summary	Supported	Vendor-shaped view	Vendor-shaped view	Neighbour session state.
show ip bgp neighbors	Supported	Vendor-shaped view	Vendor-shaped view	Neighbour details.
show ip bgp neighbors <ip> received-routes	Supported	Partial	Partial	Requires inbound storage / modelled RIB-In.
show ip bgp neighbors <ip> advertised-routes	Supported	Partial	Partial	Post-policy RIB-Out view.
show ip bgp peer-group	Supported	n/a	Partial	Shows peer-group templates and bindings.
show ip bgp confederation	Supported	n/a	Partial	Shows confederation state.

Behaviour notes

BGP timers are simulated in the event queue. The engine does not sleep for real keepalive or hold timers; it schedules deterministic events so tests, labs, and shared URLs replay consistently.

Policy is applied in the same direction users expect: inbound policy affects what enters the local BGP table, and outbound policy affects what the peer sees. received-routes and advertised-routes are useful because they let you inspect both sides of that boundary.

Route-map matching is deliberately concrete. Prefix-lists match prefixes, AS-path ACLs match the printed AS_PATH representation, standard community-lists match exact community values, and expanded community-lists use JavaScript regular expressions against the printed asn:value form. Cisco’s special _ AS-path/community regex boundary syntax is not emulated.

Graceful restart keeps stale paths available during the configured restart window. That makes it useful for protocol-behaviour labs, but it is still a model, not a reproduction of every vendor’s restart helper edge case.

VPNv4 is designed around practical L3VPN reachability: VRF route distinguishers make otherwise-overlapping prefixes unique, route targets control import/export, and MP-BGP carries the VPN route between PEs.

Examples

Basic eBGP

configure terminal
router bgp 65001
 bgp router-id 1.1.1.1
 neighbor 10.0.12.2 remote-as 65002
 address-family ipv4
  network 192.168.1.0 mask 255.255.255.0
  neighbor 10.0.12.2 activate
end
show ip bgp summary
show ip bgp

Vendor styles

IOS-style

router bgp 65001
 bgp router-id 1.1.1.1
 neighbor 10.0.12.2 remote-as 65002
 address-family ipv4
  network 192.0.2.0 mask 255.255.255.0
  neighbor 10.0.12.2 activate
  neighbor 10.0.12.2 route-map CUSTOMER-IN in

Junos-style

set routing-options router-id 1.1.1.1
set routing-options autonomous-system 65001
set protocols bgp group EBGP type external
set protocols bgp group EBGP peer-as 65002
set protocols bgp group EBGP neighbor 10.0.12.2 import CUSTOMER-IN
set policy-options policy-statement CUSTOMER-IN then local-preference 200

VyOS-style

set protocols bgp system-as 65001
set protocols bgp parameters router-id 1.1.1.1
set protocols bgp neighbor 10.0.12.2 remote-as 65002
set protocols bgp address-family ipv4-unicast network 192.0.2.0/24
set protocols bgp neighbor 10.0.12.2 address-family ipv4-unicast route-map import CUSTOMER-IN

Set LOCAL_PREF inbound

configure terminal
route-map PREFER-R2 permit 10
 set local-preference 200
router bgp 65001
 neighbor 10.0.12.2 route-map PREFER-R2 in
end
show ip bgp

Prepend AS_PATH outbound

configure terminal
route-map PREPEND-OUT permit 10
 set as-path prepend 65001 65001 65001
router bgp 65001
 neighbor 10.0.12.2 route-map PREPEND-OUT out
end
show ip bgp neighbors 10.0.12.2 advertised-routes

Tag and match a community

configure terminal
ip community-list standard CUSTOMER-A permit 65001:100
route-map TAG-OUT permit 10
 set community 65001:100 additive
route-map ACCEPT-CUSTOMER-A permit 10
 match community CUSTOMER-A
router bgp 65001
 neighbor 10.0.12.2 route-map TAG-OUT out
end

Configure a route reflector client

configure terminal
router bgp 65000
 neighbor 10.0.1.2 remote-as 65000
 neighbor 10.0.1.2 route-reflector-client
 neighbor 10.0.2.2 remote-as 65000
 neighbor 10.0.2.2 route-reflector-client
end
show ip bgp summary

Enable graceful restart

configure terminal
router bgp 65000
 bgp graceful-restart
 bgp graceful-restart restart-time 240
 bgp graceful-restart stalepath-time 600
end
show ip bgp summary

Runnable labs

Lab	Covers	Link
BGP local preference	Inbound policy and best-path preference	Open lab
BGP AS-path prepend	Outbound route-map policy and AS_PATH length	Open lab
BGP community tag and filter	Standard communities and community-list policy	Open lab
BGP MED	MED as same-neighbour-AS tiebreak	Open lab
BGP expanded community-list	Regex matching against printed community values	Open lab

Known limits

netverdict does not aim to reproduce every vendor BGP daemon edge case.

The current model does not implement add-path, full route flap damping, RPKI/origin validation, every vendor-specific default, or every AFI/SAFI a production router can carry. Aggregate-address is accepted and emitted, but aggregate route origination is not yet active in the FIB programmer.

Use this page as a support contract for the simulator’s BGP behaviour: precise where it says supported, explicit where it is partial, and quiet about things that are not modelled yet.