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c8a6b9a3d1
Old AS path maching supposes thath AS number appears only once in AS path, but that is not true. It also contains some bugs related to AS path sets. New code does not use any assumptions about semantic structure of AS path. It is asymptotically slower than the old code, but on real paths it is not significant. It also allows '?' for matching one arbitrary AS number.
451 lines
8.2 KiB
C
451 lines
8.2 KiB
C
/*
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* BIRD -- Path Operations
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*
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* (c) 2000 Martin Mares <mj@ucw.cz>
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* (c) 2000 Pavel Machek <pavel@ucw.cz>
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*
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* Can be freely distributed and used under the terms of the GNU GPL.
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*/
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#include "nest/bird.h"
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#include "nest/route.h"
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#include "nest/attrs.h"
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#include "lib/resource.h"
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#include "lib/unaligned.h"
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#include "lib/string.h"
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/* Global AS4 support, shared by all BGP instances.
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* This specifies whether BA_AS_PATH attributes contain 2 or 4 B per ASN
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*/
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int bgp_as4_support = 1;
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static void
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put_as(byte *data, u32 as)
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{
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if (bgp_as4_support)
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put_u32(data, as);
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else if (as <= 0xFFFF)
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put_u16(data, as);
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else
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bug("put_as: Try to put 32bit AS to 16bit AS Path");
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}
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static inline u32
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get_as(byte *data)
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{
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return bgp_as4_support ? get_u32(data) : get_u16(data);
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}
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struct adata *
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as_path_prepend(struct linpool *pool, struct adata *olda, u32 as)
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{
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int bs = bgp_as4_support ? 4 : 2;
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struct adata *newa;
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if (olda->length && olda->data[0] == AS_PATH_SEQUENCE && olda->data[1] < 255)
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/* Starting with sequence => just prepend the AS number */
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{
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int nl = olda->length + bs;
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newa = lp_alloc(pool, sizeof(struct adata) + nl);
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newa->length = nl;
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newa->data[0] = AS_PATH_SEQUENCE;
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newa->data[1] = olda->data[1] + 1;
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memcpy(newa->data + bs + 2, olda->data + 2, olda->length - 2);
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}
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else /* Create new path segment */
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{
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int nl = olda->length + bs + 2;
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newa = lp_alloc(pool, sizeof(struct adata) + nl);
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newa->length = nl;
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newa->data[0] = AS_PATH_SEQUENCE;
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newa->data[1] = 1;
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memcpy(newa->data + bs + 2, olda->data, olda->length);
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}
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put_as(newa->data + 2, as);
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return newa;
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}
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int
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as_path_convert_to_old(struct adata *path, byte *dst, int *new_used)
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{
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byte *src = path->data;
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byte *src_end = src + path->length;
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byte *dst_start = dst;
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u32 as;
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int i, n;
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*new_used = 0;
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while (src < src_end)
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{
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n = src[1];
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*dst++ = *src++;
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*dst++ = *src++;
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for(i=0; i<n; i++)
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{
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as = get_u32(src);
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if (as > 0xFFFF)
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{
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as = AS_TRANS;
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*new_used = 1;
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}
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put_u16(dst, as);
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src += 4;
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dst += 2;
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}
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}
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return dst - dst_start;
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}
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int
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as_path_convert_to_new(struct adata *path, byte *dst, int req_as)
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{
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byte *src = path->data;
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byte *src_end = src + path->length;
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byte *dst_start = dst;
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u32 as;
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int i, t, n;
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while ((src < src_end) && (req_as > 0))
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{
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t = *src++;
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n = *src++;
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if (t == AS_PATH_SEQUENCE)
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{
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if (n > req_as)
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n = req_as;
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req_as -= n;
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}
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else // t == AS_PATH_SET
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req_as--;
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*dst++ = t;
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*dst++ = n;
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for(i=0; i<n; i++)
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{
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as = get_u16(src);
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put_u32(dst, as);
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src += 2;
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dst += 4;
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}
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}
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return dst - dst_start;
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}
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void
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as_path_format(struct adata *path, byte *buf, unsigned int size)
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{
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int bs = bgp_as4_support ? 4 : 2;
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byte *p = path->data;
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byte *e = p + path->length;
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byte *end = buf + size - 16;
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int sp = 1;
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int l, isset;
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while (p < e)
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{
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if (buf > end)
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{
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strcpy(buf, " ...");
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return;
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}
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isset = (*p++ == AS_PATH_SET);
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l = *p++;
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if (isset)
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{
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if (!sp)
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*buf++ = ' ';
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*buf++ = '{';
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sp = 0;
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}
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while (l-- && buf <= end)
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{
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if (!sp)
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*buf++ = ' ';
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buf += bsprintf(buf, "%u", get_as(p));
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p += bs;
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sp = 0;
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}
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if (isset)
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{
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*buf++ = ' ';
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*buf++ = '}';
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sp = 0;
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}
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}
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*buf = 0;
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}
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int
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as_path_getlen(struct adata *path)
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{
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int bs = bgp_as4_support ? 4 : 2;
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int res = 0;
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u8 *p = path->data;
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u8 *q = p+path->length;
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int len;
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while (p<q)
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{
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switch (*p++)
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{
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case AS_PATH_SET: len = *p++; res++; p += bs * len; break;
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case AS_PATH_SEQUENCE: len = *p++; res += len; p += bs * len; break;
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default: bug("as_path_getlen: Invalid path segment");
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}
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}
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return res;
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}
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int
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as_path_get_first(struct adata *path, u32 *orig_as)
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{
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int bs = bgp_as4_support ? 4 : 2;
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int found = 0;
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u32 res = 0;
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u8 *p = path->data;
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u8 *q = p+path->length;
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int len;
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while (p<q)
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{
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switch (*p++)
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{
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case AS_PATH_SET:
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if (len = *p++)
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{
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found = 1;
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res = get_as(p);
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p += bs * len;
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}
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break;
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case AS_PATH_SEQUENCE:
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if (len = *p++)
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{
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found = 1;
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res = get_as(p + bs * (len - 1));
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p += bs * len;
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}
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break;
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default: bug("as_path_get_first: Invalid path segment");
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}
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}
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*orig_as = res;
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return found;
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}
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int
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as_path_get_last(struct adata *path, u32 *last_as)
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{
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u8 *p = path->data;
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if ((path->length == 0) || (p[0] != AS_PATH_SEQUENCE) || (p[1] == 0))
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return 0;
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else
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{
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*last_as = get_as(p+2);
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return 1;
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}
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}
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int
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as_path_is_member(struct adata *path, u32 as)
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{
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int bs = bgp_as4_support ? 4 : 2;
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u8 *p = path->data;
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u8 *q = p+path->length;
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int i, n;
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while (p<q)
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{
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n = p[1];
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p += 2;
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for(i=0; i<n; i++)
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{
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if (get_as(p) == as)
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return 1;
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p += bs;
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}
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}
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return 0;
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}
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struct pm_pos
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{
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u8 set;
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u8 mark;
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union
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{
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char *sp;
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u32 asn;
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} val;
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};
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static int
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parse_path(struct adata *path, struct pm_pos *pos)
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{
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int bs = bgp_as4_support ? 4 : 2;
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u8 *p = path->data;
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u8 *q = p + path->length;
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struct pm_pos *opos = pos;
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int i, j, len;
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while (p < q)
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switch (*p++)
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{
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case AS_PATH_SET:
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pos->set = 1;
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pos->mark = 0;
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pos->val.sp = p;
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len = *p;
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p += 1 + bs * len;
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pos++;
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break;
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case AS_PATH_SEQUENCE:
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len = *p++;
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for (i = 0; i < len; i++)
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{
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pos->set = 0;
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pos->mark = 0;
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pos->val.asn = get_as(p);
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p += bs;
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pos++;
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}
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break;
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default:
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bug("as_path_match: Invalid path component");
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}
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return pos - opos;
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}
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static int
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pm_match(struct pm_pos *pos, u32 asn)
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{
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if (! pos->set)
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return pos->val.asn == asn;
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int bs = bgp_as4_support ? 4 : 2;
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u8 *p = pos->val.sp;
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int len = *p++;
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int i;
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for (i = 0; i < len; i++)
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if (get_as(p + i * bs) == asn)
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return 1;
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return 0;
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}
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static void
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pm_mark(struct pm_pos *pos, int i, int plen, int *nl, int *nh)
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{
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int j;
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if (pos[i].set)
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pos[i].mark = 1;
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for (j = i + 1; (j < plen) && pos[j].set && (! pos[j].mark); j++)
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pos[j].mark = 1;
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pos[j].mark = 1;
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/* We are going downwards, therefore every mark is
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new low and just the first mark is new high */
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*nl = i + (pos[i].set ? 0 : 1);
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if (*nh < 0)
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*nh = j;
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}
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/* AS path matching is nontrivial. Because AS path can
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* contain sets, it is not a plain wildcard matching. A set
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* in an AS path is interpreted as it might represent any
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* sequence of AS numbers from that set (possibly with
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* repetitions). So it is also a kind of a pattern,
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* more complicated than a path mask.
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*
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* The algorithm for AS path matching is a variant
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* of nondeterministic finite state machine, where
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* positions in AS path are states, and items in
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* path mask are input for that finite state machine.
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* During execution of the algorithm we maintain a set
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* of marked states - a state is marked if it can be
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* reached by any walk through NFSM with regard to
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* currently processed part of input. When we process
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* next part of mask, we advance each marked state.
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* We start with marked first position, when we
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* run out of marked positions, we reject. When
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* we process the whole mask, we accept iff final position
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* (auxiliary position after last real position in AS path)
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* is marked.
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*/
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int
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as_path_match(struct adata *path, struct f_path_mask *mask)
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{
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struct pm_pos pos[2048 + 1];
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int plen = parse_path(path, pos);
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int l, h, i, nh, nl;
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/* l and h are bound of interval of positions where
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are marked states */
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pos[plen].set = 0;
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pos[plen].mark = 0;
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l = h = 0;
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pos[0].mark = 1;
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while (mask)
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{
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/* We remove this mark to not step after pos[plen] */
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pos[plen].mark = 0;
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switch (mask->kind)
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{
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case PM_ASTERISK:
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for (i = l; i <= plen; i++)
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pos[i].mark = 1;
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h = plen;
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break;
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case PM_QUESTION:
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case PM_ASN:
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nh = -1;
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for (i = h; i >= l; i--)
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if (pos[i].mark)
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{
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pos[i].mark = 0;
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if ((mask->kind == PM_QUESTION) || pm_match(pos + i, mask->val))
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pm_mark(pos, i, plen, &nl, &nh);
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}
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if (nh < 0)
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return 0;
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h = nh;
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l = nl;
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break;
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}
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mask = mask->next;
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}
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return pos[plen].mark;
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}
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