Добрый день. @korotinsv
Если я правильно понял вопрос.
R1:
ip route-static 0.0.0.0 0.0.0.0 NULL0
#
bgp 65000
router-id 1.1.1.1
peer 10.0.12.2 as-number 65000
peer 10.0.13.3 as-number 65000
#
ipv4-family unicast
undo synchronization
default-route imported
import-route static
peer 10.0.12.2 enable
peer 10.0.13.3 enable
R2:
ip route-static 0.0.0.0 0.0.0.0 NULL0
#
bgp 65000
router-id 2.2.2.2
peer 10.0.12.1 as-number 65000
peer 10.0.23.3 as-number 65000
#
ipv4-family unicast
undo synchronization
default-route imported
import-route static
peer 10.0.12.1 enable
peer 10.0.23.3 enable
R3:
bgp 65000
router-id 3.3.3.3
peer 10.0.13.1 as-number 65000
peer 10.0.23.2 as-number 65000
#
ipv4-family unicast
undo synchronization
peer 10.0.13.1 enable
peer 10.0.23.2 enable

тест1:
<R3>display bgp routing-table
BGP Local router ID is 3.3.3.3
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 0.0.0.0 10.0.13.1 0 100 0 ?
* i 10.0.23.2 0 100 0 ?
<R3>
<R3>dis fib 0.0.0.0
Route Entry Count: 1
Destination/Mask Nexthop Flag TimeStamp Interface TunnelID
0.0.0.0/0 10.0.13.1 DGU t[963] Eth0/0/1 0x0
<R3>
тест2:
R3:
bgp 65000
maximum load-balancing 2
<R3>display bgp routing-table
BGP Local router ID is 3.3.3.3
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 0.0.0.0 10.0.13.1 0 100 0 ?
* i 10.0.23.2 0 100 0 ?
<R3>
<R3>display fib 0.0.0.0
Route Entry Count: 2
Destination/Mask Nexthop Flag TimeStamp Interface TunnelID
0.0.0.0/0 10.0.13.1 DGU t[1507] Eth0/0/1 0x0
0.0.0.0/0 10.0.23.2 DGU t[1507] Eth0/0/0 0x0
<R3>
Комментарий
Команда maximum load-balancing добавляет дополнительные записи в FIB, а не в BGP Local-RIB.
Как видно по выводу FIB балансировка при такой конфигурации будет работать.