isis: set ATT bit in L1 LSPs when connected to L2 backbone

This is necessary for L1 routers within the same area to compute
default routes to reach inter-area destinations.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

holo-isis/src/instance.rs

@@ -23,7 +23,7 @@ use holo_utils::{Receiver, Sender, UnboundedReceiver, UnboundedSender};
 use ipnetwork::IpNetwork;
 use tokio::sync::mpsc;
 
-use crate::adjacency::Adjacency;
+use crate::adjacency::{Adjacency, AdjacencyState};
 use crate::collections::{Arena, Interfaces, Lsdb, LspEntryId};
 use crate::debug::{
     Debug, InstanceInactiveReason, InterfaceInactiveReason, LspPurgeReason,
@@ -496,6 +496,19 @@ impl MessageReceiver<ProtocolInputMsg> for ProtocolInputChannelsRx {
 // ===== impl InstanceUpView =====
 
 impl InstanceUpView<'_> {
+    // Checks if the instance is attached to the Level 2 backbone.
+    pub(crate) fn is_l2_attached_to_backbone(
+        &self,
+        interfaces: &Interfaces,
+        adjacencies: &Arena<Adjacency>,
+    ) -> bool {
+        interfaces
+            .iter()
+            .flat_map(|iface| iface.adjacencies(adjacencies))
+            .filter(|adj| adj.state == AdjacencyState::Up)
+            .any(|adj| adj.level_usage.intersects(LevelNumber::L2))
+    }
+
     pub(crate) fn schedule_lsp_origination(
         &mut self,
         level_type: impl Into<LevelType>,

holo-isis/src/lsdb.rs

@@ -29,7 +29,7 @@ use crate::packet::tlv::{
     ExtIpv4Reach, ExtIsReach, Ipv4Reach, Ipv6Reach, IsReach, MAX_NARROW_METRIC,
     Nlpid,
 };
-use crate::packet::{LanId, LevelNumber, LspId};
+use crate::packet::{LanId, LevelNumber, LevelType, LspId};
 use crate::spf::SpfType;
 use crate::tasks::messages::input::LspPurgeMsg;
 use crate::{spf, tasks};
@@ -149,6 +149,8 @@ fn lsp_build(
 
 fn lsp_build_flags(
     instance: &mut InstanceUpView<'_>,
+    arenas: &InstanceArenas,
+    level: LevelNumber,
     lsp_id: LspId,
 ) -> LspFlags {
     let mut lsp_flags = LspFlags::default();
@@ -158,6 +160,15 @@ fn lsp_build_flags(
     if instance.config.level_type.intersects(LevelNumber::L2) {
         lsp_flags.insert(LspFlags::IS_TYPE2);
     }
+    if instance.config.level_type == LevelType::All
+        && level == LevelNumber::L1
+        && lsp_id.pseudonode == 0
+        && lsp_id.fragment == 0
+        && instance
+            .is_l2_attached_to_backbone(&arenas.interfaces, &arenas.adjacencies)
+    {
+        lsp_flags.insert(LspFlags::ATT);
+    }
     if instance.config.overload_status
         && lsp_id.pseudonode == 0
         && lsp_id.fragment == 0
@@ -410,7 +421,7 @@ fn lsp_build_fragments(
             .get_by_lspid(&arenas.lsp_entries, &lsp_id)
             .map(|(_, lse)| lse.data.seqno + 1)
             .unwrap_or(LSP_INIT_SEQNO);
-        let lsp_flags = lsp_build_flags(instance, lsp_id);
+        let lsp_flags = lsp_build_flags(instance, arenas, level, lsp_id);
         let fragment = Lsp::new(
             level,
             instance.config.lsp_lifetime,