Commit 586c1800 authored by Ondřej Zajíček's avatar Ondřej Zajíček

Nest: Neighbor cache cleanups

Simplify neighbor cache code, fix several minor bugs, and improve
handling of ONLINK flag.
parent 45f28d85
Pipeline #37418 failed with stages
in 4 minutes and 44 seconds
...@@ -974,7 +974,7 @@ interpret(struct f_inst *what) ...@@ -974,7 +974,7 @@ interpret(struct f_inst *what)
case SA_GW: case SA_GW:
{ {
ip_addr ip = v1.val.ip; ip_addr ip = v1.val.ip;
neighbor *n = neigh_find(rta->src->proto, &ip, 0); neighbor *n = neigh_find(rta->src->proto, ip, NULL, 0);
if (!n || (n->scope == SCOPE_HOST)) if (!n || (n->scope == SCOPE_HOST))
runtime( "Invalid gw address" ); runtime( "Invalid gw address" );
......
...@@ -230,4 +230,11 @@ mem_hash(void *p, uint s) ...@@ -230,4 +230,11 @@ mem_hash(void *p, uint s)
return mem_hash_value(&h); return mem_hash_value(&h);
} }
static inline uint
ptr_hash(void *ptr)
{
uintptr_t p = (uintptr_t) ptr;
return p ^ (p << 8) ^ (p >> 16);
}
#endif #endif
...@@ -124,29 +124,21 @@ typedef struct neighbor { ...@@ -124,29 +124,21 @@ typedef struct neighbor {
ip_addr addr; /* Address of the neighbor */ ip_addr addr; /* Address of the neighbor */
struct ifa *ifa; /* Ifa on related iface */ struct ifa *ifa; /* Ifa on related iface */
struct iface *iface; /* Interface it's connected to */ struct iface *iface; /* Interface it's connected to */
struct iface *ifreq; /* Requested iface, NULL for any */
struct proto *proto; /* Protocol this belongs to */ struct proto *proto; /* Protocol this belongs to */
void *data; /* Protocol-specific data */ void *data; /* Protocol-specific data */
unsigned aux; /* Protocol-specific data */ uint aux; /* Protocol-specific data */
unsigned flags; u16 flags; /* NEF_* flags */
int scope; /* Address scope, -1 for unreachable sticky neighbors, s16 scope; /* Address scope, -1 for unreachable neighbors,
SCOPE_HOST when it's our own address */ SCOPE_HOST when it's our own address */
} neighbor; } neighbor;
#define NEF_STICKY 1 #define NEF_STICKY 1
#define NEF_ONLINK 2 #define NEF_ONLINK 2
#define NEF_BIND 4 /* Used internally for neighbors bound to an iface */ #define NEF_IFACE 4 /* Entry for whole iface */
#define NEF_IFACE 8 /* Neighbors bound to iface */
neighbor *neigh_find(struct proto *, ip_addr *, unsigned flags);
neighbor *neigh_find2(struct proto *p, ip_addr *a, struct iface *ifa, unsigned flags);
neighbor *neigh_find_iface(struct proto *p, struct iface *ifa);
static inline int neigh_connected_to(struct proto *p, ip_addr *a, struct iface *i) neighbor *neigh_find(struct proto *p, ip_addr a, struct iface *ifa, uint flags);
{
neighbor *n = neigh_find(p, a, 0);
return n && n->iface == i;
}
void neigh_dump(neighbor *); void neigh_dump(neighbor *);
void neigh_dump_all(void); void neigh_dump_all(void);
......
...@@ -2,6 +2,8 @@ ...@@ -2,6 +2,8 @@
* BIRD -- Neighbor Cache * BIRD -- Neighbor Cache
* *
* (c) 1998--2000 Martin Mares <mj@ucw.cz> * (c) 1998--2000 Martin Mares <mj@ucw.cz>
* (c) 2008--2018 Ondrej Zajicek <santiago@crfreenet.org>
* (c) 2008--2018 CZ.NIC z.s.p.o.
* *
* Can be freely distributed and used under the terms of the GNU GPL. * Can be freely distributed and used under the terms of the GNU GPL.
*/ */
...@@ -10,32 +12,38 @@ ...@@ -10,32 +12,38 @@
* DOC: Neighbor cache * DOC: Neighbor cache
* *
* Most routing protocols need to associate their internal state data with * Most routing protocols need to associate their internal state data with
* neighboring routers, check whether an address given as the next hop * neighboring routers, check whether an address given as the next hop attribute
* attribute of a route is really an address of a directly connected host * of a route is really an address of a directly connected host and which
* and which interface is it connected through. Also, they often need to * interface is it connected through. Also, they often need to be notified when
* be notified when a neighbor ceases to exist or when their long awaited * a neighbor ceases to exist or when their long awaited neighbor becomes
* neighbor becomes connected. The neighbor cache is there to solve all * connected. The neighbor cache is there to solve all these problems.
* these problems.
* *
* The neighbor cache maintains a collection of neighbor entries. Each * The neighbor cache maintains a collection of neighbor entries. Each entry
* entry represents one IP address corresponding to either our directly * represents one IP address corresponding to either our directly connected
* connected neighbor or our own end of the link (when the scope of the * neighbor or our own end of the link (when the scope of the address is set to
* address is set to %SCOPE_HOST) together with per-neighbor data belonging to a * %SCOPE_HOST) together with per-neighbor data belonging to a single protocol.
* single protocol. * A neighbor entry may be bound to a specific interface, which is required for
* link-local IP addresses and optional for global IP addresses.
* *
* Active entries represent known neighbors and are stored in a hash * Neighbor cache entries are stored in a hash table, which is indexed by triple
* table (to allow fast retrieval based on the IP address of the node) and * (protocol, IP, requested-iface), so if both regular and iface-bound neighbors
* two linked lists: one global and one per-interface (allowing quick * are requested, they are represented by two neighbor cache entries. Active
* processing of interface change events). Inactive entries exist only * entries are also linked in per-interface list (allowing quick processing of
* when the protocol has explicitly requested it via the %NEF_STICKY * interface change events). Inactive entries exist only when the protocol has
* flag because it wishes to be notified when the node will again become * explicitly requested it via the %NEF_STICKY flag because it wishes to be
* a neighbor. Such entries are enqueued in a special list which is walked * notified when the node will again become a neighbor. Such entries are instead
* whenever an interface changes its state to up. Neighbor entry VRF * linked in a special list, which is walked whenever an interface changes its
* association is implied by respective protocol. * state to up. Neighbor entry VRF association is implied by respective
* protocol.
*
* Besides the already mentioned %NEF_STICKY flag, there is also %NEF_ONLINK,
* which specifies that neighbor should be considered reachable on given iface
* regardless of associated address ranges, and %NEF_IFACE, which represents
* pseudo-neighbor entry for whole interface (and uses %IPA_NONE IP address).
* *
* When a neighbor event occurs (a neighbor gets disconnected or a sticky * When a neighbor event occurs (a neighbor gets disconnected or a sticky
* inactive neighbor becomes connected), the protocol hook neigh_notify() * inactive neighbor becomes connected), the protocol hook neigh_notify() is
* is called to advertise the change. * called to advertise the change.
*/ */
#undef LOCAL_DEBUG #undef LOCAL_DEBUG
...@@ -43,126 +51,151 @@ ...@@ -43,126 +51,151 @@
#include "nest/bird.h" #include "nest/bird.h"
#include "nest/iface.h" #include "nest/iface.h"
#include "nest/protocol.h" #include "nest/protocol.h"
#include "lib/hash.h"
#include "lib/resource.h" #include "lib/resource.h"
#define NEIGH_HASH_SIZE 256 #define NEIGH_HASH_SIZE 256
#define NEIGH_HASH_OFFSET 24 #define NEIGH_HASH_OFFSET 24
static slab *neigh_slab; static slab *neigh_slab;
static list sticky_neigh_list, iface_neigh_list, neigh_hash_table[NEIGH_HASH_SIZE]; static list neigh_hash_table[NEIGH_HASH_SIZE], sticky_neigh_list;
static inline uint static inline uint
neigh_hash(struct proto *p, ip_addr *a) neigh_hash(struct proto *p, ip_addr a, struct iface *i)
{ {
return (p->hash_key ^ ipa_hash(*a)) >> NEIGH_HASH_OFFSET; return (p->hash_key ^ ipa_hash(a) ^ ptr_hash(i)) >> NEIGH_HASH_OFFSET;
} }
static int static int
if_connected(ip_addr *a, struct iface *i, struct ifa **ap) if_connected(ip_addr a, struct iface *i, struct ifa **ap, uint flags)
{ {
struct ifa *b; struct ifa *b;
/* Handle iface pseudo-neighbors */
if (flags & NEF_IFACE)
return *ap = NULL, (i->flags & IF_UP) ? SCOPE_HOST : -1;
/* Host addresses match even if iface is down */
WALK_LIST(b, i->addrs)
if (ipa_equal(a, b->ip))
return *ap = b, SCOPE_HOST;
/* Rest do not match if iface is down */
if (!(i->flags & IF_UP)) if (!(i->flags & IF_UP))
{ return *ap = NULL, -1;
*ap = NULL;
return -1;
}
/* Regular neighbors */
WALK_LIST(b, i->addrs) WALK_LIST(b, i->addrs)
{
if (b->flags & IA_PEER)
{ {
*ap = b; if (ipa_equal(a, b->opposite))
return *ap = b, b->scope;
if (ipa_equal(*a, b->ip)) }
return SCOPE_HOST; else
if (b->flags & IA_PEER) {
{ if (ipa_in_netX(a, &b->prefix))
if (ipa_equal(*a, b->opposite)) {
return b->scope; /* Do not allow IPv4 network and broadcast addresses */
} if (ipa_is_ip4(a) &&
else (net_pxlen(&b->prefix) < (IP4_MAX_PREFIX_LENGTH - 1)) &&
{ (ipa_equal(a, net_prefix(&b->prefix)) || /* Network address */
if (ipa_in_netX(*a, &b->prefix)) ipa_equal(a, b->brd))) /* Broadcast */
{ return *ap = NULL, -1;
/* Do not allow IPv4 network and broadcast addresses */
if (ipa_is_ip4(*a) && return *ap = b, b->scope;
(net_pxlen(&b->prefix) < (IP4_MAX_PREFIX_LENGTH - 1)) &&
(ipa_equal(*a, net_prefix(&b->prefix)) || /* Network address */
ipa_equal(*a, b->brd))) /* Broadcast */
{
*ap = NULL;
return -1;
}
return b->scope;
}
}
} }
}
}
/* Handle ONLINK flag */
if (flags & NEF_ONLINK)
return *ap = NULL, ipa_classify(a) & IADDR_SCOPE_MASK;
*ap = NULL; return *ap = NULL, -1;
return -1;
} }
/** static inline int
* neigh_find - find or create a neighbor entry. if_connected_any(ip_addr a, struct iface *vrf, struct iface **iface, struct ifa **addr, uint flags)
* @p: protocol which asks for the entry.
* @a: pointer to IP address of the node to be searched for.
* @flags: 0 or %NEF_STICKY if you want to create a sticky entry.
*
* Search the neighbor cache for a node with given IP address. If
* it's found, a pointer to the neighbor entry is returned. If no
* such entry exists and the node is directly connected on
* one of our active interfaces, a new entry is created and returned
* to the caller with protocol-dependent fields initialized to zero.
* If the node is not connected directly or *@a is not a valid unicast
* IP address, neigh_find() returns %NULL.
*/
neighbor *
neigh_find(struct proto *p, ip_addr *a, unsigned flags)
{ {
return neigh_find2(p, a, NULL, flags); struct iface *i;
} struct ifa *b;
int s, scope = -1;
*iface = NULL;
*addr = NULL;
/* Get first match, but prefer SCOPE_HOST to other matches */
WALK_LIST(i, iface_list)
if ((!vrf || vrf == i->master) && ((s = if_connected(a, i, &b, flags)) >= 0))
if ((scope < 0) || ((scope > SCOPE_HOST) && (s == SCOPE_HOST)))
{
*iface = i;
*addr = b;
scope = s;
}
return scope;
}
/**
* neigh_find - find or create a neighbor entry
* @p: protocol which asks for the entry
* @a: IP address of the node to be searched for
* @iface: optionally bound neighbor to this iface (may be NULL)
* @flags: %NEF_STICKY for sticky entry, %NEF_ONLINK for onlink entry
*
* Search the neighbor cache for a node with given IP address. Iface can be
* specified for link-local addresses or for cases, where neighbor is expected
* on given interface. If it is found, a pointer to the neighbor entry is
* returned. If no such entry exists and the node is directly connected on one
* of our active interfaces, a new entry is created and returned to the caller
* with protocol-dependent fields initialized to zero. If the node is not
* connected directly or *@a is not a valid unicast IP address, neigh_find()
* returns %NULL.
*/
neighbor * neighbor *
neigh_find2(struct proto *p, ip_addr *a, struct iface *ifa, unsigned flags) neigh_find(struct proto *p, ip_addr a, struct iface *iface, uint flags)
{ {
neighbor *n; neighbor *n;
int class, scope = -1; int class, scope = -1;
uint h = neigh_hash(p, a); uint h = neigh_hash(p, a, iface);
struct iface *i; struct iface *ifreq = iface;
struct ifa *addr; struct ifa *addr = NULL;
WALK_LIST(n, neigh_hash_table[h]) /* Search the cache */ WALK_LIST(n, neigh_hash_table[h]) /* Search the cache */
if (n->proto == p && ipa_equal(*a, n->addr) && (!ifa || (ifa == n->iface))) if ((n->proto == p) && ipa_equal(n->addr, a) && (n->ifreq == iface))
return n; return n;
class = ipa_classify(*a); if (flags & NEF_IFACE)
if (class < 0) /* Invalid address */ {
return NULL; if (ipa_nonzero(a) || !iface)
if (((class & IADDR_SCOPE_MASK) == SCOPE_HOST) || return NULL;
(((class & IADDR_SCOPE_MASK) == SCOPE_LINK) && (ifa == NULL)) || }
!(class & IADDR_HOST)) else
return NULL; /* Bad scope or a somecast */ {
class = ipa_classify(a);
if (class < 0) /* Invalid address */
return NULL;
if (((class & IADDR_SCOPE_MASK) == SCOPE_HOST) ||
(((class & IADDR_SCOPE_MASK) == SCOPE_LINK) && !iface) ||
!(class & IADDR_HOST))
return NULL; /* Bad scope or a somecast */
}
if (ifa) if ((flags & NEF_ONLINK) && !iface)
{ return NULL;
scope = if_connected(a, ifa, &addr);
flags |= NEF_BIND;
if ((scope < 0) && (flags & NEF_ONLINK)) if (iface)
scope = class & IADDR_SCOPE_MASK; {
} scope = if_connected(a, iface, &addr, flags);
iface = (scope < 0) ? NULL : iface;
}
else else
WALK_LIST(i, iface_list) scope = if_connected_any(a, p->vrf, &iface, &addr, flags);
if ((!p->vrf || p->vrf == i->master) &&
((scope = if_connected(a, i, &addr)) >= 0))
{
ifa = i;
break;
}
/* scope < 0 means i don't know neighbor */ /* scope < 0 means i don't know neighbor */
/* scope >= 0 implies ifa != NULL */ /* scope >= 0 <=> iface != NULL */
if ((scope < 0) && !(flags & NEF_STICKY)) if ((scope < 0) && !(flags & NEF_STICKY))
return NULL; return NULL;
...@@ -170,52 +203,15 @@ neigh_find2(struct proto *p, ip_addr *a, struct iface *ifa, unsigned flags) ...@@ -170,52 +203,15 @@ neigh_find2(struct proto *p, ip_addr *a, struct iface *ifa, unsigned flags)
n = sl_alloc(neigh_slab); n = sl_alloc(neigh_slab);
memset(n, 0, sizeof(neighbor)); memset(n, 0, sizeof(neighbor));
n->addr = *a; add_tail(&neigh_hash_table[h], &n->n);
if (scope >= 0) add_tail((scope >= 0) ? &iface->neighbors : &sticky_neigh_list, &n->if_n);
{ n->addr = a;
add_tail(&neigh_hash_table[h], &n->n);
add_tail(&ifa->neighbors, &n->if_n);
}
else
{
add_tail(&sticky_neigh_list, &n->n);
scope = -1;
}
n->iface = ifa;
n->ifa = addr; n->ifa = addr;
n->iface = iface;
n->ifreq = ifreq;
n->proto = p; n->proto = p;
n->data = NULL;
n->aux = 0;
n->flags = flags; n->flags = flags;
n->scope = scope; n->scope = scope;
return n;
}
neighbor *
neigh_find_iface(struct proto *p, struct iface *ifa)
{
neighbor *n;
node *nn;
/* We keep neighbors with NEF_IFACE foremost in ifa->neighbors list */
WALK_LIST2(n, nn, ifa->neighbors, if_n)
{
if (! (n->flags & NEF_IFACE))
break;
if (n->proto == p)
return n;
}
n = sl_alloc(neigh_slab);
memset(n, 0, sizeof(neighbor));
add_tail(&iface_neigh_list, &n->n);
add_head(&ifa->neighbors, &n->if_n);
n->iface = ifa;
n->proto = p;
n->flags = NEF_IFACE;
n->scope = (ifa->flags & IF_UP) ? SCOPE_HOST : -1;
return n; return n;
} }
...@@ -224,30 +220,26 @@ neigh_find_iface(struct proto *p, struct iface *ifa) ...@@ -224,30 +220,26 @@ neigh_find_iface(struct proto *p, struct iface *ifa)
* neigh_dump - dump specified neighbor entry. * neigh_dump - dump specified neighbor entry.
* @n: the entry to dump * @n: the entry to dump
* *
* This functions dumps the contents of a given neighbor entry * This functions dumps the contents of a given neighbor entry to debug output.
* to debug output.
*/ */
void void
neigh_dump(neighbor *n) neigh_dump(neighbor *n)
{ {
debug("%p %I ", n, n->addr); debug("%p %I %s %s ", n, n->addr,
if (n->iface) n->iface ? n->iface->name : "[]",
debug("%s ", n->iface->name); n->ifreq ? n->ifreq->name : "[]");
else
debug("[] ");
debug("%s %p %08x scope %s", n->proto->name, n->data, n->aux, ip_scope_text(n->scope)); debug("%s %p %08x scope %s", n->proto->name, n->data, n->aux, ip_scope_text(n->scope));
if (n->flags & NEF_STICKY) if (n->flags & NEF_STICKY)
debug(" STICKY"); debug(" STICKY");
if (n->flags & NEF_IFACE) if (n->flags & NEF_ONLINK)
debug(" IFACE"); debug(" ONLINK");
debug("\n"); debug("\n");
} }
/** /**
* neigh_dump_all - dump all neighbor entries. * neigh_dump_all - dump all neighbor entries.
* *
* This function dumps the contents of the neighbor cache to * This function dumps the contents of the neighbor cache to debug output.
* debug output.
*/ */
void void
neigh_dump_all(void) neigh_dump_all(void)
...@@ -256,73 +248,109 @@ neigh_dump_all(void) ...@@ -256,73 +248,109 @@ neigh_dump_all(void)
int i; int i;
debug("Known neighbors:\n"); debug("Known neighbors:\n");
WALK_LIST(n, sticky_neigh_list)
neigh_dump(n);
WALK_LIST(n, iface_neigh_list)
neigh_dump(n);
for(i=0; i<NEIGH_HASH_SIZE; i++) for(i=0; i<NEIGH_HASH_SIZE; i++)
WALK_LIST(n, neigh_hash_table[i]) WALK_LIST(n, neigh_hash_table[i])
neigh_dump(n); neigh_dump(n);
debug("\n"); debug("\n");
} }
static inline void
neigh_notify(neighbor *n)
{
if (n->proto->neigh_notify && (n->proto->proto_state != PS_STOP))
n->proto->neigh_notify(n);
}
static void static void
neigh_up(neighbor *n, struct iface *i, int scope, struct ifa *a) neigh_up(neighbor *n, struct iface *i, struct ifa *a, int scope)
{ {
DBG("Waking up sticky neighbor %I\n", n->addr); DBG("Waking up sticky neighbor %I\n", n->addr);
n->iface = i; n->iface = i;
n->ifa = a; n->ifa = a;
n->scope = scope; n->scope = scope;
if (! (n->flags & NEF_IFACE)) rem_node(&n->if_n);
{ add_tail(&i->neighbors, &n->if_n);
add_tail(&i->neighbors, &n->if_n);
rem_node(&n->n);
add_tail(&neigh_hash_table[neigh_hash(n->proto, &n->addr)], &n->n);
}
if (n->proto->neigh_notify && (n->proto->proto_state != PS_STOP)) neigh_notify(n);
n->proto->neigh_notify(n);
} }
static void static void
neigh_down(neighbor *n) neigh_down(neighbor *n)
{ {
DBG("Flushing neighbor %I on %s\n", n->addr, n->iface->name); DBG("Flushing neighbor %I on %s\n", n->addr, n->iface->name);
if (! (n->flags & (NEF_BIND | NEF_IFACE))) n->iface = NULL;
n->iface = NULL;
n->ifa = NULL; n->ifa = NULL;
n->scope = -1; n->scope = -1;
if (! (n->flags & NEF_IFACE)) rem_node(&n->if_n);
{ add_tail(&sticky_neigh_list, &n->if_n);
rem_node(&n->if_n);
rem_node(&n->n);
}
if (n->proto->neigh_notify && (n->proto->proto_state != PS_STOP)) neigh_notify(n);
n->proto->neigh_notify(n); }
if (n->flags & NEF_STICKY) static inline void
neigh_free(neighbor *n)
{
rem_node(&n->n);
rem_node(&n->if_n);
sl_free(neigh_slab, n);
}
/**
* neigh_update: update neighbor entry w.r.t. change on specific iface
* @n: neighbor to update
* @iface: changed iface
*
* The function recalculates state of the neighbor entry @n assuming that only
* the interface @iface may changed its state or addresses. Then, appropriate
* actions are executed (the neighbor goes up, down, up-down, or just notified).
*/
void
neigh_update(neighbor *n, struct iface *iface)
{
struct ifa *ifa = NULL;
int scope = -1;
/* Iface-bound neighbors ignore other ifaces */
if (n->ifreq && (n->ifreq != iface))
return;
/* VRF-bound neighbors ignore changes in other VRFs */
if (n->proto->vrf && (n->proto->vrf != iface->master))
return;
scope = if_connected(n->addr, iface, &ifa, n->flags);
/* When neighbor is going down, try to respawn it on other ifaces */
if ((scope < 0) && (n->scope >= 0) && !n->ifreq && (n->flags & NEF_STICKY))
scope = if_connected_any(n->addr, n->proto->vrf, &iface, &ifa, n->flags);
/* No change or minor change - ignore or notify */
if ((scope == n->scope) && (iface == n->iface))
{
if (ifa != n->ifa)
{ {
add_tail(&sticky_neigh_list, &n->n); n->ifa = ifa;
neigh_notify(n);
/* Respawn neighbor if there is another matching prefix */
struct iface *i;
struct ifa *a;
int scope;
if (!n->iface)
WALK_LIST(i, iface_list)
if ((scope = if_connected(&n->addr, i, &a)) >= 0)
{
neigh_up(n, i, scope, a);
return;
}
} }
if (! (n->flags & (NEF_STICKY | NEF_IFACE))) return;
sl_free(neigh_slab, n); }
/* Major change - going down and/or going up */
if (n->scope >= 0)
neigh_down(n);
if ((n->scope < 0) && !(n->flags & NEF_STICKY))
{
neigh_free(n);
return;
}
if (scope >= 0)
neigh_up(n, iface, ifa, scope);
} }
...@@ -338,21 +366,11 @@ neigh_down(neighbor *n) ...@@ -338,21 +366,11 @@ neigh_down(neighbor *n)
void void
neigh_if_up(struct iface *i) neigh_if_up(struct iface *i)
{ {
struct ifa *a;
neighbor *n; neighbor *n;
node *x, *y; node *x, *y;
int scope;
/* Wake up all iface neighbors */ WALK_LIST2_DELSAFE(n, x, y, sticky_neigh_list, if_n)
WALK_LIST2_DELSAFE(n, x, y, i->neighbors, if_n) neigh_update(n, i);
if ((n->scope < 0) && (n->flags & NEF_IFACE))
neigh_up(n, i, SCOPE_HOST, NULL);
/* Wake up appropriate sticky neighbors */
WALK_LIST_DELSAFE(n, x, sticky_neigh_list)
if ((!n->iface || n->iface == i) &&
((scope = if_connected(&n->addr, i, &a)) >= 0))
neigh_up(n, i, scope, a);
} }
/** /**
...@@ -361,8 +379,7 @@ neigh_if_up(struct iface *i) ...@@ -361,8 +379,7 @@ neigh_if_up(struct iface *i)
* *
* Notify the neighbor cache that an interface has ceased to exist. * Notify the neighbor cache that an interface has ceased to exist.
* *
* It causes all entries belonging to neighbors connected to this interface * It causes all neighbors connected to this interface to be updated or removed.
* to be flushed.
*/ */
void