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--- wiki:bgp_ip_transit_info [2026/01/08 14:52] – [gobgp software example] add info about adding private IP antisa
+++ wiki:bgp_ip_transit_info [2026/04/13 09:46] (current) – [References] add netactuate link antisa
@@ Line 79: / Line 79: @@
 //peer-as// is peer ASN, also given by provider.
+Provider might also give you a //multihop-ttl// value. If this is the case you need to [[https://github.com/osrg/gobgp/blob/master/docs/sources/ebgp-multihop.md|add]] the following to both ipv4 and ipv6  configuration to above (change the value):
+<code>
+[neighbors.ebgp-multihop.config]
+    enabled = true
+    multihop-ttl = 64
+</code>
 After starting gobgp you should see the session is established:
@@ Line 157: / Line 166: @@
 </WRAP>
+===== Checking propagation =====
+RIPE has BG play tool to check the history of route propagation here https://stat.ripe.net/bgplay/ and https://stat.ripe.net/lg.
+{{:wiki:screenshots:2026:02:ripe_bgplay.png?direct&600|}}
+Here's an example of Tzulo server provider which advertises to multiple upstreams
+https://bgp.he.net/AS11878#_graph4
+https://bgp.tools/as/11878#connectivity
+which has multiple arrows pointing to upstreams.
+===== Updating AS path length =====
+When advertising IP from multiple providers, one can have a shorter AS path and take all the traffic for itself. You can adjust the length of the AS path on your side by prepending your AS number 1 or more times to extend the path.
+Example using gobgp:
+<code>
+[global.config]
+...
+[global.apply-policy.config]
+export-policy-list = ["prepend_as_path"]
+default-import-policy = "accept-route"
+default-export-policy = "accept-route"
+[[neighbors]]
+...
+...
+[[policy-definitions]]
+name = "prepend_as_path"
+  [[policy-definitions.statements]]
+  name = "stmt_prepend"
+    [policy-definitions.statements.actions]
+      route-disposition = "accept-route"
+    # number of times to prepend our asn. This allows for controlling
+    # the length of th AS path that packet takes so it affects routing
+    # https://www.noction.com/blog/as-path-and-as-path-prepending
+    [policy-definitions.statements.actions.bgp-actions.set-as-path-prepend]
+      as = "203619"
+      repeat-n = 1
+</code>
+Here we're prepending the path 1 additional time. After restarting the service notice a repeating ASN in //AS_PATH// column
+   # gobgp neighbor 213.155.129.101 adj-out
+   ID  Network              Next Hop             AS_PATH              AttrsFiltered
+   89.124.253.0/24      185.229.190.69       203619 203619        [{Origin: ?}]not filtered
+On RIPE Looking glass this will be shown as
+{{:wiki:screenshots:2026:02:ripe_lg.png?direct&600|}}
 ====== Tested on ======
   * gobgp_version: 4.2.0
@@ Line 167: / Line 229: @@
   * https://cs249i.stanford.edu/projects/project_1.pdf
   * https://www.noction.com/blog/bgp-anycast
+  * https://render.com/blog/how-to-build-an-anycast-network
+  * https://datatracker.ietf.org/doc/html/rfc4271#autoid-1
+  * https://www.noction.com/blog/as-path-and-as-path-prepending
+  * https://www.netactuate.com/docs/guides/mixed-provider-anycast