Commit 106c347a2a for frr

commit 106c347a2a33a7a3563996b1cfdb460858b1761c
Author: Gabriel Goller <g.goller@proxmox.com>
Date:   Wed Oct 28 10:07:06 2026 +0100

    isisd: warn about area tags that exceed the RLFA limit

    Tags longer than 31 bytes are truncated in local RLFA messages, which
    can prevent replies from being matched to the IS-IS instance. Warn users
    while still accepting these tags to not break existing setups.

    Signed-off-by: Gabriel Goller <g.goller@proxmox.com>

diff --git a/isisd/isis_cli.c b/isisd/isis_cli.c
index 038d82acf2..6c8f38241b 100644
--- a/isisd/isis_cli.c
+++ b/isisd/isis_cli.c
@@ -49,8 +49,13 @@ DEFPY_YANG_NOSH(router_isis, router_isis_cmd,
 	nb_cli_enqueue_change(vty, ".", NB_OP_CREATE, NULL);

 	ret = nb_cli_apply_changes(vty, "%s", base_xpath);
-	if (ret == CMD_SUCCESS)
+	if (ret == CMD_SUCCESS) {
 		VTY_PUSH_XPATH(ISIS_NODE, base_xpath);
+		/* lib/zclient.h: zapi_rlfa_igp.isis.area_tag is 32 bytes, including NUL. */
+		if (strlen(tag) > 31)
+			vty_out(vty,
+				"Warning: IS-IS area tags longer than 31 bytes are truncated in remote LFA messages and may prevent remote LFA from working.\n");
+	}

 	return ret;
 }