Shared Explicit Style

Assume a tunnel is created between R0 and R5 which are some hops apart.

First tunnel is created with BW = 100 and the tunnel is UP. Now if we increase the BW to a higher value such that the constraints are not met due to BW limitation on the path, ie; the head router is not able to find a path to tunnel destination with the configured BW value, the tunnel will not go down.

But, if we do “shut” and then “no shut”, the tunnel will never come up due to signalling failure.

This behaviour is due to “Shared Explicit(SE)” Style. It ensure the make-before-break rule. Here in this case, the tunnel is already UP with low BW. So, now if we increase the BW of the tunnel, the current tunnel will not go down until a new TE LSP is found with the configured constraints.
R0#show mpls traffic-eng tunnels tunnel 5
Name: R0_t5                               (Tunnel5) Destination: 5.5.5.5
Status:
Admin: up         Oper: up     Path: valid       Signalling: connected
path option 2, type dynamic (Basis for Setup, path weight 21)
Config Parameters:
Bandwidth: 100      kbps (Global) Priority: 7  7   Affinity: 0x0/0xFFFF
Metric Type: TE (default)
AutoRoute:  disabled  LockDown: disabled  Loadshare: 100      bw-based
auto-bw: disabled
InLabel  :  –
OutLabel : FastEthernet0/1, 17
<snip>
R0(config)#int tu 5
R0(config-if)#tunnel mpls traffic-eng bandwidth 100000
R0#show mpls traffic-eng tunnels tunnel 5
Name: R0_t5                               (Tunnel5) Destination: 5.5.5.5
Status:
Admin: up         Oper: up     Path: valid       Signalling: connected
path option 2, type dynamic (Basis for Setup, path weight 21)
Change in required resources detected: reroute pending
Currently Signalled Parameters:
Bandwidth: 100      kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
Metric Type: TE (default)
Config Parameters:
Bandwidth: 100000   kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
Metric Type: TE (default)
AutoRoute:  disabled  LockDown: disabled  Loadshare: 100000   bw-based
auto-bw: disabled
If we shut/no shut, the tunnel line protocol stays down as the head end router cannot signal a tunnel with the configured BW.
R0(config)#int tu 5
R0(config-if)#shutdown
R0(config-if)#
*Mar  1 03:06:59.943: %LINK-5-CHANGED: Interface Tunnel5, changed state to administratively down
*Mar  1 03:07:00.943: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel5, changed state to down
R0(config-if)#no shutdown
R0(config-if)#
*Mar  1 03:07:05.983: %LINK-3-UPDOWN: Interface Tunnel5, changed state to up
*Mar  1 03:07:06.983: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel5, changed state to up
R0(config-if)#
*Mar  1 03:07:20.735: %LINEPROTO-5-UPDOWN: Line protocol on Interface Tunnel5, changed state to down
R0(config-if)#
R0(config-if)#do show mpls traff tunnel tunn 5
Name: R0_t5                               (Tunnel5) Destination: 5.5.5.5
Status:
Admin: up         Oper: down Path: not valid   Signalling: Down
path option 2, type dynamic
Config Parameters:
Bandwidth: 100000   kbps (Global)  Priority: 7  7   Affinity: 0x0/0xFFFF
Metric Type: TE (default)
AutoRoute:  disabled  LockDown: disabled  Loadshare: 100000   bw-based
auto-bw: disabled
Shortest Unconstrained Path Info:
Path Weight: 21 (TE)
Explicit Route: 12.1.1.1 12.1.1.2 10.1.1.1 10.1.1.2
10.1.3.1 10.1.3.2 5.5.5.5
History:
Tunnel:
Time since created: 50 minutes, 55 seconds
Time since path change: 45 seconds
Prior LSP:
ID: path option 2 [78]
Removal Trigger: tunnel shutdown
Last Error: PCALC:: No path to destination, 5.5.5.5
R0(config-if)#
SE style will be present  in  RESV message as shown in the below debug.
R0#debug ip rsvp dump-messages resv
RSVP dump-messages debugging is on
R0#
*Mar  1 02:54:53.259: RSVP:     version:1 flags:0000 type:Resv cksum:A600 ttl:255 reserved:0 length:108
*Mar  1 02:54:53.267:  SESSION              type 7 length 16:
*Mar  1 02:54:53.271:   Destination 3.3.3.3, TunnelId 3, Source 100.100.100.100, Protocol 0, Flags 0000
*Mar  1 02:54:53.271:  HOP                  type 1 length 12:
*Mar  1 02:54:53.275:   Neighbor 12.1.1.2, LIH 0x03000403
*Mar  1 02:54:53.275:  TIME_VALUES          type 1 length 8 :
*Mar  1 02:54:53.279:   Refresh period is 30000 msecs
*Mar  1 02:54:53.279:  STYLE                type 1 length 8 :
*Mar  1 02:54:53.279:   Shared-Explicit (SE)
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